Disposable cassette for intravascular heat exchange catheter

ABSTRACT

A heat exchange fluid supply system for supplying a heat exchange fluid to an intravascular heat exchange catheter includes a disposable cassette having a bulkhead and an external heat exchanger, and which is configured to operate in combination with a reusable master control unit The bulkhead includes a reservoir section and a pump section. The reservoir section is provided with a means to monitor the amount of heat exchange fluid that is in the system. The bulkhead provides the mechanism for priming the system with heat exchange fluid from an external source and for circulating fluid to the catheter in a closed circuit. The pump section is configured to allow for pumping of heat exchange fluid at a constant pressure.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-In-Part of U.S. patentapplication Ser. No. 09/138,830, filed on Aug. 24, 1998; and claims thebenefit of U.S. Provisional Application No. 60/185,561, filed on Feb.28, 2000.

TECHNICAL FIELD

[0002] The present invention is directed to a fluid supply and fluidhandling mechanism for an intravascular heat exchanger, and moreparticularly to a disposable cassette with a pump head and an externalheat exchanger for use as a system to provide hot or cold heat transferfluid to an intravascular heat exchange catheter.

BACKGROUND

[0003] Under ordinary circumstances, thermoregulatory mechanisms existin the healthy human body to maintain the body at a constant temperatureof about 37° C. (98.6° F.), a condition sometimes referred to asnormothermia. To maintain normothermia, the thermoregulatory mechanismsact so that heat lost to the environment is replaced by the same amountof heat generated by metabolic activity in the body.

[0004] For various reasons, however, a person may accidentally develop abody temperature that is above or below normal, conditions known ashyperthermia or hypothermia respectively. These conditions havegenerally been regarded as harmful and patients suffering from eithercondition have been treated to return them to normothermia by variousmechanisms, including application of warming or cooling blankets,administration of hot or cold liquids by mouth, hot or cold liquidsinfused into the bloodstream, immersion of the patient in hot or coldbaths, and directly heating or cooling blood during cardiopulmonarybypass.

[0005] Besides treating undesirable hypothermia to reverse the conditionand restore normothermia, medical science recognizes that it issometimes valuable to intentionally induce and maintain regional orwhole body hypothermia for therapeutic reasons. The term “whole bodyhypothermia” refers to the condition where the whole body temperature,usually measured as the core body temperature, is below normothermia.“Regional hypothermia” refers to the condition where target tissue ofone region of the body such as the brain or the heart is maintained at atemperature below normothermia. During regional hypothermia, the corebody temperature may be normothermic, or may be slightly hypothermic butis generally warmer than the target tissue.

[0006] It may be desirable, for example, to induce whole body orregional hypothermia for the purpose of treating, or minimizing theadverse effects of, certain neurological diseases or disorders such ashead trauma, spinal trauma and hemorrhagic or ischemic stroke.Additionally, it is sometimes desirable to induce whole body or regionalhypothermia for the purpose of facilitating or minimizing adverseeffects of certain surgical or interventional procedures such as openheart surgery, aneurysm repair surgeries, endovascular aneurysm repairprocedures, spinal surgeries, or other surgeries where blood flow to thebrain, spinal cord or vital organs may be interrupted or compromised.Neural tissue such as the brain or spinal cord, is particularly subjectto damage by blood deprivation for any reason including ischemic orhemorrhagic stroke, cardiac arrest, intracerebral or intracranialhemorrhage, and head trauma In each of these instances, damage to braintissue may occur because of brain ischemia, increased intracranialpressure, edema or other processes, often resulting in a loss ofcerebral function and permanent neurological deficits. Hypothermia hasalso been found to be advantageous to protect cardiac muscle tissueduring or after ischemia, for example during heart surgery or during orafter a myocardial infarct.

[0007] Traditional methods inducing and/or maintaining hypothermiainclude application of surface cooling such as an ice bath or coolingblankets, infusing cold liquid into the vascular system of a patient, orcontrolling the temperature of a patient's blood during cardiopulmonarybypass. While each of these may be useful in certain settings, they eachhave significant disadvantages. For example, inducing hypothermia byplacing a patient into a cold bath lacks precise control over apatient's core temperature and thus may result in harmful overshoot,which may be difficult if not impossible to reverse with any degree ofcontrol. It generally cannot be used in conjunction with surgery becausesterility and access to the patient's body may make its use impracticalor impossible. Cooling blankets are often too slow to cool the patient,or simply unable to overcome the body's natural ability to generateheat, particularly if the patient is shivering or experiencingvasoconstriction. Even if the patient is anesthetized, or has otherwisehad his thermoregulatory responses impaired or eliminated, cooling bymeans of cooling blankets is still often too slow and inefficient to beuseful. Control over the patient's temperature is generally poor, whichis particularly dangerous if the patient's own thermoregulatory controlsare eliminated or impaired.

[0008] Infusion of cold or hot fluid into a patient's bloodstream hasalso been used to affect the temperature of a patient. However, thisprocedure is severely limited because of the hazards of fluid loading.Particularly where hypothermia is to be maintained for a long period oftime, continuous infusion of sufficient cold liquid to counter the heatgenerated by ordinary bodily activity creates an unacceptable amount offluid introduced into the body. In addition, as with the methodsdescribed above, control over the patient temperature is limited.

[0009] Another method sometimes employed, especially during heartsurgery, is cardiopulmonary bypass, where blood is removed from thebody, oxygenated and returned to the circulatory system by means of amechanical pump. While being circulated outside the body, thetemperature of the blood may be controlled by directly heating orcooling it and then pumping it back into the body, and in this way thetemperature of the entire body of the patient may be controlled. Becauseof the large volume of blood removed, treated, and pumped back into thebody, heating or cooling the body by means of cardiopulmonary bypass isvery rapid and may be precisely controlled. However, the use of anexternal mechanical pump to circulate blood tends to be very destructiveof the blood and thus physicians try to minimize the time on which theblood is being subjected to this treatment, preferably to four hours orless. Furthermore, the situations in which the use of this method fortemperature control is very limited because of the extremely invasivenature of cardiopulmonary bypass. The patient must be anesthetized,highly trained personnel are required, and the procedure is onlyavailable in an operating room or similarly equipped facility.

[0010] Intravascular heat exchangers have been developed to controlpatient temperature for either treating hypothermia or hyperthermia orinducing and maintaining hypothermia The intravascular heat exchangerovercomes many of the shortcomings of the above mentioned methods whilepermitting the advantageous aspects of controlling patient temperature.The intravascular heat exchanger comprises a catheter in which heattransfer fluid is circulated between an external heat exchanger, such asa solid state thermoelectric plate of one or more Peltier cooling unitsand a heat transfer region such as a balloon region on the end of thecatheter. The heat exchange region is inserted into the vasculature of apatient. The heat transfer fluid exchanges heat with the blood at theheat transfer region to change the temperature of the blood and thus ofthe patient. The heat transfer fluid is then circulated out of the bodyand exchanges heat with the external heat exchanger outside the body toadd or remove the heat lost or gained from the blood. In this manner thetemperature of the blood and ultimately of the patient may be controlledby controlling the temperature of the external heat exchanger.

[0011] Some intravascular heat exchange catheters may be designed toaffect a small amount of tissue, for example a small bolus of blood inthermodilution catheters (see e.g. Williams, U.S. Pat. No. 4,941,475) orcatheters designed to protect or affect the tissue in contact with thecatheter (see e.g. Neilson, et al., U.S. Pat. No. 5,733,319). However,intravascular heat exchangers designed to affect whole or regional bodytemperature may be expected to exchange a significant amount of energy,for example more than 100 watts. This is achieved by maintaining amaximum difference in temperature between the blood and the heattransfer region (ΔT), and flowing a maximum amount of heat exchangefluid through the circuit. A heat exchange fluid that can be maintainedbetween 0° C. and 45° C. is generally preferable, along with a fluidsupply system that can supply adequate flow of heat transfer fluid andtemperature control of that fluid. Such systems ideally will also haveone of more of the following properties: maximum external heat exchangeability, closed circuit for sterility, small volume for precise andrapid control of temperature, a system for pressure regulation toprecisely control flow rate, optimal flow rate, disposable features,ease of handling, and reliability.

SUMMARY OF THE INVENTION

[0012] One aspect of the invention is a heat exchange fluid supplysystem for supplying a heat exchange fluid to an intravascular heatexchange catheter, which includes a disposable cassette having a pumphead and an external heat exchanger. The configuration of the externalheat exchanger is not intended to be structurally limited and mayinclude a sack-like configuration, a relatively flat configuration withmultiple paths therein, with a long serpentine path therein, or anyother suitable configuration capable of mating with a heat generating orremoving unit. The system may be configured to operate in combinationwith a reusable master control unit and an external fluid source.

[0013] Another aspect of the invention is a disposable cassette forsupplying a heat exchange fluid to a heat exchange catheter, thecassette comprising: an external heat exchanger comprising a flowchannel having an inlet and an outlet; a first fluid supply line, thefirst fluid supply line being in fluid communication with the flowchannel inlet; a pump head contained in the disposable fluid supplycassette, and having a pump inlet and a pump outlet, where the pumpinlet is in fluid communication with the external heat exchanger flowchannel outlet for pumping fluid from the external heat exchanger flowchannel outlet; a second fluid supply line, the second fluid supply linebeing in fluid communication with the pump outlet for receiving fluidpumped out of the pump outlet; and a pressure regulator, the pressureregulator being in fluid communication with the pump outlet forregulating the pressure of fluid pumped from the pump head.

[0014] Yet another aspect of the invention is a heat exchange fluidsupply system for a heat exchange catheter, the system comprising: anexternal heat exchanger comprising a structural member and a compliantmember, where the compliant member is sealed to the structural member ina pattern, the pattern forming a flow channel between the compliantmember and the structural member, and the flow channel having an inletand an outlet; a first fluid supply line, the first fluid supply linebeing in fluid communication with the flow channel inlet; a bulkhead,the bulkhead comprising a pump head and a reservoir, the reservoirhaving a reservoir inlet and a reservoir outlet, the reservoir inletbeing in fluid communication with the external heat exchanger flowchannel outlet, the pump head having a pump inlet and a pump outlet, thepump inlet being in fluid communication with the reservoir outlet forpumping fluid from the reservoir outlet; a second fluid supply line, thesecond fluid supply line being in fluid communication with the pumpoutlet for receiving fluid pumped out of the pump outlet; and anexternal fluid source, the external fluid source being in fluidcommunication with the bulkhead.

[0015] Still another aspect of the invention is a disposable cassettefor supplying heat exchange fluid to a heat exchange catheter, thecassette comprising: an external heat exchanger having an inlet and anoutlet; a first fluid supply line, the first fluid supply line in fluidcommunication with the heat exchanger inlet; a disposable pump headcontained in the cassette, the pump head actuated by an electric motor,the pump head having an inlet and an outlet, and the pump inlet being influid communication with the heat exchanger outlet; a second fluidsupply line, the second fluid supply line being in fluid communicationwith the pump outlet for receiving fluid pumped out of the pump outlet;and an optional pressure regulator, the pressure regulator being influid communication with the pump outlet for regulating the pressure offluid pumped from said pump head.

[0016] Another aspect of the invention is a disposable cassette forsupplying a heat exchange fluid to an intravascular heat exchangecatheter, the cassette having a bulkhead and an external heat exchanger.The external heat exchanger has a thin heat exchanger layer and a backplate fused together to form a serpentine flow channel or a plurality offlow channels, and has an inlet orifice and an outlet orifice that allowfluid to circulate through the external heat exchanger and whichcommunicate with the bulkhead. In one embodiment, the bulkhead has threecomponents which can be independent sections coupled together or whereat least two of the sections are housed together: a reservoir section, afeedblock section and a pump section. The reservoir section has an inlethole leading from the external heat exchanger and an outlet leading tothe feedblock section, a fluid reservoir for storage of heat exchangefluid, a fluid level detector for monitoring the level of heat exchangefluid within the fluid reservoir, a cover plate that functions to retainfluid within the reservoir and which is fitted with at least one venthole into which is positioned a hydrophobic vent for releasing aircontained within the fluid reservoir. The feedblock section has acentral chamber which houses a priming valve that directs fluid flow, aninlet and corresponding inlet channel from the reservoir and an inletand corresponding inlet channel from an external fluid source which bothlead into the central chamber, an outflow channel leading from thecentral chamber to an outlet which is directed to the pump head, aflexible membrane covering the central chamber, a flow-through channelhaving an inlet which leads from the pump head and a fluid couplingoutlet means for fluidly connecting the catheter to the bulkhead, and aflow-through channel having a fluid coupling inlet means for fluidlyconnecting the catheter to the bulkhead and an outlet which leads to thepump section and then to the external heat exchanger. The pump sectionhas a quasi-cardioid shaped cavity, into which is positioned a rotor isfitted with a vane for moving fluid from an inlet and inlet channel toan outlet channel and outlet, a wheel assembly to facilitate movement ofthe rotor and a flow-through channel having an inlet that leads from thefeedblock section and an outlet which leads to the external heatexchanger.

[0017] In yet another aspect of the invention, the bulkhead has twocomponents: a reservoir section and a pump section, where the pump andreservoir sections are configured similar to that described above,except that the outlet of the reservoir section leads to the pumpsection and the reservoir further comprises a pressure damper and aninlet in fluid communication with an external fluid source.

[0018] Still another aspect of the invention relates to a cassette forsupplying heat exchange fluid to a heat exchange catheter, where thecassette comprises: (a) an external heat exchanger comprising astructural member and a compliant member, where the compliant member issealed to the structural member in a pattern that forms a flow channelbetween the compliant member and the structural member, and where theflow channel has an inlet and an outlet; (b) a first fluid supply linein fluid communication with the flow channel inlet; (c) a bulkheadcomprising a reservoir and a disposable pump head, where the reservoircontains an inlet in fluid communication with the flow channel outlet,and further has a fluid level detector for detecting the level of fluidwithin the reservoir, wherein the pump head is a cardioid vane pump headhaving an inlet and an outlet, and the pump head is actuated by anelectric motor, where the pump inlet is in fluid communication with thereservoir outlet and the electric motor is controlled by an amplifiercontroller, where the amplifier controller supplies a constant currentto the pump head thereby causing the pump head to supply a relativelyconstant pressure to the fluid in the second fluid supply line; (d) asecond fluid supply line in fluid communication with the pump outlet forreceiving fluid pumped out of the pump outlet; (e) an external fluidsource in fluid communication with the reservoir; and (f) a pressuredamper in fluid communication with the pump outlet.

[0019] Another aspect of the invention pertains to a method forproviding a temperature regulated source of heat exchange fluid for heatexchange catheters, comprising the steps of: providing a circuitcomprising an external heat exchanger, a pump, a heat exchange catheter,and air vents, where the external heat exchanger, pump and heat exchangecatheter are in fluid communication such that fluid pumped by the pumpis circulated through the heat exchange catheter and the external heatexchanger, and the air vents allow passage of gas in and out of thecircuit through the vents but do not allow passage of liquid in and outof the circuit though the air vents; providing a heat generating orremoving unit in heat exchange relationship with the external heatexchanger; providing an external fluid source in fluid communicationwith the circuit; circulating heat exchange fluid from the externalsource through the circuit by means of pumping with the pump whilesimultaneously venting any gas contained in the circuit out through theair vents; and controlling the temperature of the heat exchanger fluidin the circuit by controlling the temperature of the heat generating orremoving unit.

BRIEF DESCRIPTION OF THE DRAWING

[0020]FIG. 1 is an illustration of the disposable fluid supply cassetteof the invention attached to a heat exchange catheter, external fluidsource and positioned for insertion into a suitable reusable mastercontrol unit.

[0021]FIG. 2 is an illustration of the disposable fluid supply cassetteand a reusable master control unit.

[0022]FIGS. 3 and 4 are exploded views of different embodiments of thedisposable fluid supply cassette of the invention.

[0023]FIG. 4A is a perspective bottom view of a fitment of theinvention.

[0024]FIG. 4B is a perspective top view of a fitment of the invention.

[0025]FIG. 4C is a cross-section of the external heat exchanger takenalong line 4C-4C of FIG. 4 with no pressurized fluid therein.

[0026]FIG. 4D is a cross-section of the external heat exchanger takenalong line 4C-4C of FIG. 4 with pressurized fluid therein.

[0027]FIG. 5 is a top plan view of the bulkhead of the disposable fluidsupply cassette of FIG. 3.

[0028]FIG. 5A illustrates the fluid flow pathway.

[0029]FIG. 5B is a cross-sectional view of the reservoir section takenalong line 5B-5B of FIG. 5.

[0030]FIG. 6 is a top plan view of the bulkhead of the disposable fluidsupply cassette of FIG. 4.

[0031]FIG. 6A illustrates the fluid flow pathway.

[0032]FIG. 7 is an exploded view of the reservoir section of thebulkhead of FIG. 3.

[0033]FIG. 8 is an exploded view of the feedblock section of thebulkhead of FIG. 3.

[0034]FIG. 9 is an exploded view of the pump section of the bulkhead ofFIG. 3.

[0035]FIG. 10 is an exploded view of the reservoir section of thebulkhead of FIG. 4.

[0036]FIG. 11A is a cross-sectional view of a priming valve of theinvention shown with the valve stem relaxed and the valve in the normaloperating position.

[0037]FIG. 11B is a cross-sectional view of a priming valve of theinvention shown with the valve stem depressed and the valve in theauto-prep position.

[0038]FIG. 12A is a top plan view of the pump section of the invention.

[0039]FIG. 12B illustrates the geometry of the pump section.

[0040]FIG. 13 is a side cutaway view of the pump head of the inventiontaken along line 13-13 of FIG. 12A.

[0041]FIG. 14 is a top cut-away view of the pump wheels in place withinthe reusable master control unit.

[0042]FIG. 15 is a side view of the pump wheels in place within thereusable master control unit.

[0043]FIG. 16 is a top view of a pressure regulator valve of theinvention.

[0044]FIG. 17 is a cross-sectional view of the throttle chamber takenalong line 17-17 of FIG. 16.

[0045]FIG. 18 is a cross-sectional view of a pressure damper.

[0046]FIGS. 19A, 19B and 19C are schematic illustrations of the fluidflow using different embodiments of the disposable fluid supply cassetteof the invention.

[0047]FIGS. 20A, 20B and 20C are side views of various embodiments ofthe pump vane.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The invention relates to a heat exchange fluid supply system forsupplying a heat exchange fluid to an intravascular heat exchangecatheter, which includes a disposable cassette having a pump head and anexternal heat exchanger. The system is configured to operate incombination with a reusable master control unit and an external fluidsource. The heat exchange fluid supply system of the invention isdesigned to provide an adequate supply of heat exchange fluid to thecatheter at sufficient flow rate and to provide a convenient andefficient heat exchange means to adjust the temperature of the heatexchange fluid. This system is easy to handle, inexpensive anddisposable, thus eliminating the need for extensive and time consumingsterilization between treatment of different patients. An additionalfeature of the cassette is that, due to its closed loop fluid path,sterility is maintained for the duration of operation of the catheter.

[0049]FIG. 1 illustrates the heat exchange fluid supply system of theinvention which includes disposable components including a heat exchangecatheter 160; a disposable heat exchange fluid supply cassette 5, whichincludes a pump head 139 and fluid housing 19; sensors 77, 78; and adual channel flow line 169; as well as reusable components including aheat generating or removing unit 11, a pump drive mechanism 12 andvarious controls for the unit.

[0050] The heat exchange catheter 160 is formed with a catheter flowline 162 and a heat exchanger 163 which may be for example a heatexchange balloon operated using closed-loop flow of heat exchangemedium. The catheter shaft may be formed with a working lumen 156 forinjection of drugs, fluoroscopic dye, or the like, and for receipt of aguide wire 157 for use in placing the heat transfer catheter at anappropriate location in the patient's body. The proximal end of theshaft may be connected to a multi-arm adapter 151 for providing separateaccess to various channels in the catheter shaft. For example, one arm152 may provide access to the working lumen 156 of the catheter shaftfor insertion of a guide wire 157 to steer the heat transfer catheter tothe desired location. Where the internal heat exchanger 163 is a heatexchange balloon for closed-loop flow of a biocompatible fluid thatserves as the heat exchange medium 35, the adapter 151 may contain anarm 153 to connect an inlet flow line 150 to an inlet flow channel (notshown) within the catheter shaft, a separate arm 154 to connect anoutlet fluid line 158 to an outlet flow channel (also not shown). Thedual channel flow line 169 may contain both the inlet and outlet flowlines 150, 158 to connect the catheter flow line 162 to the disposableheat exchange fluid supply cassette 5. Additionally, one of the flowlines, for example the inlet flow line 150 may be connected to anexternal fluid source 15 of heat exchange medium 35 to prime theclosed-loop heat exchange balloon catheter system as necessary. Theexternal fluid source 15 may also be directly connected to the cassette5, as is shown in other embodiments of the invention.

[0051] The heat exchange cassette 5 may include fluid housing 19configured in a serpentine pathway for the heat exchange fluid to bepumped through the cassette by means of a disposable pump head 139. Theheat exchange cassette, including the serpentine pathway and the pumphead 139 is configured to install into a reusable master control unit185. The master control unit may include a heat generating or removingunit 11 such as a solid state thermoelectric heater/cooler (TE cooler).A TE cooler is particularly advantageous because the same unit iscapable of either generating heat or removing heat by changing thepolarity of current activating the unit. Therefore it may beconveniently controlled to supply or remove heat from the system withoutthe need of two separate units.

[0052] The master control unit includes a pump drive mechanism 12 thatactivates the pump head 139 to pump the heat exchange fluid 35 and causeit to circulate through the catheter's heat exchanger 163 and theserpentine path of the fluid housing 19 in the heat exchange cassette.When installed, the fluid housing 19 is in thermal communication withthe TE cooler, and thus the TE cooler may act to heat or cool the heatexchange fluid as that fluid is circulated through the serpentinepathway. When the heat exchange fluid is circulated through the internalheat exchanger 163 located in a patient's body, it may act to add orremove heat from the body. In this way the TE cooler may act to affectthe blood temperature of a patient as desired.

[0053] The TE cooler and the pump head are responsive to a control unit13. The control unit receives data input through electrical connections63, 64, 65 to numerous sensors, for example body temperature sensors 77,78 that may sense temperatures from a patient's ear, brain region,bladder, rectum, esophagus or other appropriate location as desired bythe operator who places the sensors. Likewise, a sensor 82 may monitorthe temperature of the heat exchange balloon, and other sensors (notshown) may be provided as desired to monitor the blood temperature atthe distal tip of the catheter, at the proximal tip of the balloon, orother desired location.

[0054] An operator by means of the manual input unit 14 may provide theoperating parameters of the control system, for example a pre-selectedtemperature for the brain. These parameters are communicated to thecontrol unit 13 by means of a connection between the manual input unitand the control unit In practice, the operator using the manual inputunit supplies a set of parameters to the control unit. For example, adesired temperature for the brain region and/or the whole body of thepatient may be specified as the preselected temperature. Data isreceived from the sensors 77, 78 indicating for example, a sensedtemperature of the patient at the location of the sensors, e.g. theactual core body temperature of the patient or the actual temperature ofthe brain region. Other data input may include the actual temperature ofthe heat exchanger, the temperature of blood at the distal end of thecatheter body, or the like.

[0055] The control unit 13 coordinates the data and selectively actuatesthe various units of the system to achieve and maintain parameters. Forexample, it may actuate the TE cooler 11 to increase the amount of heatit is removing if the actual temperature is above the specifiedtemperature, or decreasing the amount of heat being removed if thetemperature is below the specified temperature. It may stop the pumpingof the heat exchange fluid when the body or regional temperature sensedis the desired temperature, or it may stop pumping in response to otherpre-determined criteria.

[0056] The control unit 13 may have a buffer range for operation whereina target temperature is established, and an upper variance set pointtemperature and lower variance set point temperature are also set. Inthis way, the control unit may cause the heat exchanger to operate untilthe target temperature is reached. At that temperature, the control unitmay suspend the operation of the heat exchanger until either the uppervariance set point temperature is sensed or the lower variance set pointtemperature is reached. When the upper variance set point temperature issensed, the control unit would then activate the heat exchanger toremove heat from the blood stream. On the other hand, if the lowervariance set point temperature is sensed, then the control unit wouldactivate the heat exchanger to add heat to the blood stream. Such acontrol scheme as applied to this system has the advantage of allowingthe operator to essentially dial in a desired temperature and the systemwill act to reach that target temperature and maintain the patient atthat target temperature. At the same time, a buffer range is establishedso that when the target temperature is reached, the control unit 13 willgenerally not turn the TE cooler 11 on and off or activate anddeactivate the pump drive mechanism 12 in rapid succession, actions thatwould be potentially damaging to the electric units in question.

[0057] It may also be perceived, in keeping with the present invention,that the control unit 13 may be configured to simultaneously respond toseveral sensors, or to activate or deactivate various components such asseveral heat exchangers. In this way, for example, a control unit mightheat blood that is subsequently circulated to the core body in responseto a sensed core body temperature that is below the target temperature,and simultaneously activate a second heat exchanger to cool blood thatis directed to the brain region in response to a sensed braintemperature that is above the target temperature. It may be that thesensed body temperature is at the target temperature and thus the heatexchanger that is in contact with blood circulating to the core body maybe turned off by the control unit, while at the same time the controlunit continues to activate the heat exchanger to cool blood that isdirected to the brain region. Any of the many control schemes that maybe anticipated by an operator and programmed into the control unit arecontemplated by this invention.

[0058] An advantage of the system as illustrated is that all theportions of the system that are in contact with the patient aredisposable, but substantial and relatively expensive portions of thesystem are reusable. Thus the catheter, the flow path for sterile heatexchange fluid, the sterile heat exchange fluid itself, and the pumphead are all disposable. Even if a rupture in the heat exchange balloonpermits the heat exchange fluid channels and thus the pump head to comein contact with a patient's blood, no cross-contamination will occurbetween patients because all those elements are disposable. The pumpdrive mechanism, the electronic control mechanisms, the TE cooler, andthe manual input unit, however, are all reusable for economy andconvenience. Likewise, the sensors may be disposable, but the controlunit to which they attach is reusable.

[0059] The system of FIG. 1 can also be readily modified within thescope of the instant invention. For example, but not by way oflimitation, the serpentine pathway may be a coil or other suitableconfiguration, the sensors may sense a wide variety of body locationsand other parameters may be provided to the control unit, such astemperature or pressure, the heat exchanger may be any appropriate type,such as a thermal electric heating unit which would not require thecirculation of heat exchange fluid. If a heat exchange balloon isprovided, a pump head might be provided that is a screw pump, a gearpump, diaphragm pump, a peristaltic roller pump, or any other suitablemeans for pumping the heat exchange fluid. All of these and othersubstitutions obvious to those of skill in the art are contemplated bythis invention.

[0060] In one embodiment of the invention, a disposable cassette forsupplying a heat exchange fluid to a heat exchange catheter, comprises:an external heat exchanger comprising a structural member and acompliant member, where the compliant member is sealed to the structuralmember in a pattern, and the pattern forms one or more flow channelsbetween the compliant member and the structural member, the flow channelhaving an inlet and an outlet; a first fluid supply line, the firstfluid supply line being in fluid communication with the flow channelinlet; a pump head contained in the disposable fluid supply cassette,and having a pump inlet and a pump outlet, where the pump inlet is influid communication with the external heat exchanger flow channel outletfor pumping fluid from the flow channel outlet; a second fluid supplyline, the second fluid supply line being in fluid communication with thepump outlet for receiving fluid pumped out of the pump outlet; and apressure regulator, the pressure regulator being in fluid communicationwith the pump outlet for regulating the pressure of fluid pumped fromthe pump head.

[0061] Referring to FIGS. 1-4, an exemplary disposable cassette 5 forsupplying a heat exchange fluid 35 to a heat exchange catheter 160 isshown. The cassette 5 comprises an external heat exchanger 20. Theexternal heat exchanger can any be a combination of one or morestructural and compliant members such that the overall configuration ofthe external heat exchanger is adapted to mate with the heat generatingor removing unit. In a preferred embodiment, the structural member is aback plate 26 and the compliant member is heat exchange layer 28. Theheat exchange layer is sealed to the back plate in a pattern which formsa flow channel 34 between the back plate and the heat exchange layer,and the flow channel has an inlet 36 and an outlet 38.

[0062] The cassette 5 also includes a first fluid supply line that is influid communication with the flow channel inlet 36. The pump head 139has a pump inlet 113 and a pump outlet 115, where the inlet in fluidcommunication with the external heat exchanger flow channel outlet 38and serves to pump fluid from the flow channel outlet. A second fluidsupply line is in fluid communication with the pump outlet 115 andreceives fluid that is pumped out of the outlet. The cassette 5 alsoincludes a pressure regulator that is in fluid communication with thepump outlet. The disposable cassette is configured such that when thefirst and second fluid supply lines are connected to a heat exchangecatheter, a fluid circuit is created and includes the external heatexchanger, pump head, the fluid lines and the catheter.

[0063] In another embodiment of the invention, a heat exchange fluidsupply system for a heat exchange catheter comprises: an external heatexchanger comprising a structural member and a compliant member, wherethe compliant member is sealed to the structural member in a pattern,the pattern forming a flow channel between the compliant member and thestructural member, and the flow channel having an inlet and an outlet; afirst fluid supply line, the first fluid supply line being in fluidcommunication with the flow channel inlet; a bulkhead, the bullheadcomprising a pump head and a reservoir, the reservoir having a reservoirinlet and a reservoir outlet, the reservoir inlet being in fluidcommunication with the external heat exchanger flow channel outlet, thepump head having a pump inlet and a pump outlet, the pump inlet being influid communication with the reservoir outlet for pumping fluid from thereservoir outlet; a second fluid supply line, the second fluid supplyline being in fluid communication with the pump outlet for receivingfluid pumped out of the pump outlet; and an external fluid source, theexternal fluid source being in fluid communication with the bulkhead.Referring more particularly to the cassette shown in FIGS. 3 and 4, andthe overall system of FIG. 2, this system comprises the external heatexchanger 20 and fluid supply lines as described above. In addition, thecassette comprises a bulkhead (30, 330) that comprises a pump head 140and a reservoir (58, 358). The reservoir has a reservoir inlet that isin fluid communication with the external heat exchanger flow channeloutlet 38 and a reservoir outlet (62, 362). The pump head has a pumpinlet 113 and a pump outlet 115, and the pump inlet is in fluidcommunication with the reservoir outlet (62, 362) for pumping fluid fromthe reservoir outlet. The heat exchange fluid supply system also caninclude an external fluid source 15 that is in fluid communication withthe bulkhead.

[0064] One embodiment of the invention is a heat exchange fluid supplysystem for supplying a heat exchange fluid to an intravascular heatexchange catheter, which includes a disposable cassette having abulkhead and an external heat exchanger. The bulkhead includes areservoir section and a pump section which are in fluid communicationwith each other. The reservoir section is provided with a means tomonitor the amount of heat exchange fluid that is in the system. Thesystem may optionally comprise a mechanism for priming the system withheat exchange fluid from an external source and for circulating fluid tothe catheter in a closed circuit, which is preferably a valve having afirst position whereby the system is primed with heat exchange fluidfrom an external source and a second position where the fluid iscirculated to the catheter in a closed circuit. In the absence of thisvalved-priming system, the system is passively primed. The pump sectionis configured to allow for pumping of heat exchange fluid at a constantpressure. This aspect of the invention is illustrates in FIG. 2, whichshows one embodiment of the disposable heat exchange fluid supplycassette 10 having a bulkhead 30 and an external heat exchanger havingan inlet and an outlet, depicted in FIG. 2 as external heat exchanger20. The cassette is configured to operate in combination with a reusablemaster control unit 186, which will typically be provided with a powersupply and a heat generating or removing unit, and other parts thatcooperate with the cassette 10, the details of which will be describedin detail below.

[0065] One embodiment of the cassette of the invention is shown in FIG.3 and includes a disposable fluid supply cassette 10 has an externalheat exchanger 20 coupled to a bulkhead 30 by means of a cover plate168. The bulkhead includes a reservoir section 40, an optional feedblocksection 80 and a pump section 100, the details of which are describedbelow. The sections can be independent and discrete units that arecoupled together, as shown in FIG. 2. The invention also contemplateshousing more than one section together in a single unit This may bedesired for ease in manufacturing and assembly. The sections can bemachined, molded or cast and are typically of a durable material such asplastic or Plexiglas.

[0066] The feedblock is configured to communicate with an external fluidsource 15, which can be any suitable source of biocompatible fluid, bymeans of an external fluid providing line 16. The fluid line 16 may beprovided with a pinch clamp 21. The source of biocompatible fluid can befor example, an IV bag of saline. Bag size is not critical but has atypical capacity of about 250 ml. In addition, the feedblockcommunicates with an intravascular heat exchange catheter 160, by meansof fluid supply line 150 and fluid return line 158. The external fluidproviding, fluid supply and fluid return lines are typically of aflexible compressible material such as polyvinylchloride or othersuitable flexible compressible tubing material. The disposable fluidsupply cassette 10 can be packaged with or separately from the heatexchange catheter 160.

[0067] Another embodiment of the disposable heat exchange fluid supplycassette of the invention is shown in FIG. 4. The disposable fluidsupply cassette 310 has an external heat exchanger 20 coupled to abulkhead 330 by means of a cover plate 368. The bulkhead includes areservoir section 340 and a pump section 300. The reservoir section 340is configured to communicate with the external fluid source by means ofan external fluid providing line. In addition, the pump section 300communicates with the intravascular heat exchange catheter by means of afluid supply line and a fluid return line.

[0068] The cassette of the invention is initially primed, that is,filled with heat exchange fluid from an external source and excess airremoved. This priming of the system of the invention can be accomplishedin numerous ways. One embodiment of the invention utilizes a“valved-priming” mechanism, and is illustrated by the embodiment of FIG.3. This valved-priming mechanism involves a priming sequence having avalve or the like controlling temporary fluid input from an externalfluid source, and once the system is primed, the valve prevents furtherfluid input from the external source and the fluid flow becomes a closedcircuit within the cassette 10 and the catheter 160. In the embodimentof FIG. 3, the valved-priming mechanism is contained within a discreteunit referred to as the feedblock section. It is understood however,that the valved-priming mechanism can be located in another portion ofthe bulkhead, for example as part of the pump or reservoir section, andstill serve the same function. During priming, heat exchange fluid fromexternal fluid source 15 flows through the external fluid providing line16 and enters the feedblock section 80, and then flows into the pumpsection 100. From the pump section, the fluid is pumped out throughfluid supply line 150, which is coupled to the catheter inlet of theheat exchange catheter 160. It is thereafter circulated through thecatheter, back through the fluid return line 158 to the external heatexchanger 20, through the external heat exchanger and into thereservoir. As the fluid is pumped into the reservoir, air displaced bythe fluid escapes through the hydrophobic vents 54. This generallycontinues until the system is full of heat exchange fluid and excess airhas been vented out of the system. At this point in the process, thevalve is closed from the external fluid source and the fluid supplycircuit between the catheter and the cassette is a closed circuit. Thispriming occurs prior to the insertion of the heat exchange catheter intothe patient, with the heat exchange balloon outside the body. Thevalved-priming is described in greater detail below in connection withFIGS. 5, 8, 11A and 11B.

[0069] Another embodiment of the invention utilizes a “passive-priming”mechanism and is illustrated by the embodiment of FIG. 1 and FIG. 4.This passive-priming mechanism involves fluid input from the externalfluid source 15, which serves to fill the system. The external fluidsource 15 is generally hung or placed at a location above the reservoir,and is connected by means of an external fluid providing line 16directly or indirectly to the reservoir in the cassette 310. Fluid movesinto the reservoir, the pump is activated, and as described above inconjunction with the valved-priming, the fluid is pumped through thesystem and excess air is expelled out through the hydrophobic vents 54.Once the system is primed, the amount of fluid needed to maintain thesystem in a full condition may change slightly due primarily to changesin the compliance of the system at different temperatures. Toaccommodate this, additional fluid may enter the system from theexternal fluid source to maintain the filled condition, and similarly,excess fluid may leave the system and reenter the external fluid source.This has the advantage of maintaining a relatively uniform fluid levelby automatic action. As with the valved-priming, this is generally donebefore the catheter is inserted, with the balloon outside the patient'svascular system.

[0070] As indicated above, the disposable cassette comprises an externalheat exchanger, which is formed of a combination of one or morestructural and compliant members. In a preferred embodiment, thestructural member is a stiff back plate 26 and the compliant member is aflexible heat exchange layer 28, which are fused together to form aserpentine flow channel or a plurality of flow channels, and having aninlet orifice and an outlet orifice that communicate with the bulkhead.The external heat exchanger is positioned so as to be in a heat transferrelationship with a heat generating or removing unit provided in thereusable master control unit, as shown in FIGS. 1 and 2. There arenumerous heat exchangers that can be used with the disposable cassetteof the invention. Due to the configuration of the external heatexchanger, the heat generating or removing unit is preferably a flatthermally conducting plate which is heated or cooled to add or removeheat from the heat exchange fluid.

[0071] Turning to FIG. 4, the external heat exchanger 20 is shown ashaving two layers, a relatively stiff back plate 26 that functions as astructural member and a thinner heat exchange layer 28 that functions asthe compliant member. The back plate 26 is typically made of a highdensity polyethylene and is generally about 0.030 inches (30 mils)thick. The thinner heat exchange layer is shown in this embodiment asbeing sealed in a serpentine pattern to the back plate by fusing such asby heat sealing or other suitable technique to permanently adhere thetwo layers together. The pattern of heat sealing creates a serpentinepathway composed of sealed portions 32 separating a serpentine flowchannel 34 or a plurality of flow channels. The sealed portions 32provide for the channels 34 to be continuous. The winding flow channels34 form a pathway which causes the heat exchange fluid to flow back andforth adjacent to and in heat transfer relationship with the heatgenerating or removing unit, and ensures that the fluid circulatesproximate to the heat generating or removing unit for a sufficientamount of time to allow for adequate heating or cooling of the fluid.The invention also encompasses utilizing sealed portions that are notcontinuous, as long as the sealed portions are configured so as tocreate channels that permit fluid flow through the external heatexchanger 20. In addition, the external heat exchanger can be configuredto have a V-shaped leading edge 23 that acts as a guide to facilitateplacement into the control unit 186.

[0072] The thinner heat exchange layer is generally about 4 to 8 mils,and is typically a low density polyethylene material, and is slightlyelastomeric or compliant so that when pressurized heat exchange fluid 35is placed into the legs of the channels, they bow out slightly as may beseen in FIGS. 4C (uninflated) and 4D (inflated). Since the back plate 26and thinner heat exchange layer 28 are both polyethylene, they weldtogether effectively by means of heat welding. However, the bulkhead 330is not the same material, and therefore the external heat exchanger issealed to the bulkhead by other means, such as by a mechanical pressureseal.

[0073] The external heat exchanger 20 is provided with an extendedattachment 48 whereby the external heat exchanger may be sealed to thebulkhead 330. The extended attachment 48 has three sections, a firstflap section 142, a cutaway section 144 and a second flap section 146.One or more vent holes 52 are cut into the first flap section 142 toallow air to vent from the corresponding number of hydrophobic gaspermeable vents 54 over a fluid reservoir, as will be described ingreater detail below. While a plurality of vent holes 52 is shown in theembodiment of FIG. 4, any suitable shape or number of holes willsuffice, for example a single vent hole is shown in the embodiment ofFIG. 3.

[0074] The external heat exchanger 20 also has an inlet orifice 36 andan outlet orifice 38, which allows the heat exchange fluid to exit thebulkhead, circulate through the external heat exchanger (positioned in aheat transfer relationship with a heat generating or removing unit) andthen enter the bulkhead after being heated or cooled. Each orifice isprovided with a fitment that allows fluid to flow into the space betweenthe thin heat exchange layer 28 and the back plate 26. When heatexchange fluid is pumped into the inlet orifice 36 through a firstfitment 22, it winds its way along the serpentine path to outlet orifice38 and then enters the bulkhead through a second fitment 24. The entireexternal heat exchanger is lain on a hot or cold plate of a heatgenerating or removing unit such as the heat exchange surface of athermoelectric cooler, with the thinner heat exchange layer 28positioned against the hot or cold plate. In this way, the temperatureof heat exchange fluid may be controlled by controlling the temperatureof the hot or cold plate and pumping fluid through the external heatexchanger.

[0075] Fitments 22, 24 are secured within the inlet and outlet orifices36, 38. The fitments are constructed as illustrated in FIGS. 4A and 4Bfor fitment 24. Each fitment has a bored channel, a base plate 44, and aplurality of spacer protrusions 46 on the lower surface of the baseplate. The embodiment of FIG. 4B illustrates four such protrusions butthe invention contemplates having fewer or more than four protrusions.When the fitments are placed in the external heat exchanger, the channelexits the orifice, and the base plate is tightly positioned between theheat exchange layer 28 and the back plate 26. The spacer protrusionsspace the base plate away from the back plate of the external heatexchanger so that fluid contained within channels 34 passes between theprotrusions, through fitment channel 37, and then into bulkhead 330.Similarly, fluid returning from the heat exchange catheter enterschannels 34 through a bored channel in fitment 22, passes between theprotrusions and flows into the channels. Two O-rings, such as flexiblerubber washers, can be positioned around the periphery of the topsection 148 of each fitment and are positioned between the heat exchangelayer 28 and the bulkhead 30. The reservoir section has an inlet hole56, while the pump section has an outlet hole 57. The fitment topsection 148 of fitment 24 is sized to be inserted into inlet hole 56 andthe corresponding top section of fitment 22 is sized to be inserted intooutlet hole 57.

[0076]FIGS. 7, 8 and 9 are exploded views of the bulkhead 30 of theembodiment of FIG. 3 and its components, while FIGS. 5 and 5A illustratethe assembled bulkhead 30. Similarly, FIG. 10 is an exploded view of oneof the reservoir section 340 component of the bulkhead 330 of theembodiment of FIG. 4, while FIGS. 6 and 6A illustrate the assembledbulkhead 330.

[0077] Referring to FIGS. 7, 5 and 5A, the reservoir section 40 has aninlet hole 56 leading from the external heat exchanger 20 and an outletchannel 62 leading to the feedblock section 80, a fluid reservoir 58with an indented area 60 for storage of heat exchange fluid, a fluidlevel detector 69 for monitoring the level of heat exchange fluid withinthe fluid reservoir, an optional mounting block 75 for positioning of anoptional pressure regulator valve useful for controlling the pressurefor heat exchange fluid flow from the feedblock section to the catheter,a reservoir cover plate 53 that serves to retain fluid within thereservoir. The cover plate 53 seals the reservoir but is fitted with oneor more vent holes 55 into which are positioned a corresponding numberof hydrophobic gas permeable vents 54 for releasing air contained withinthe fluid reservoir. The reservoir section 40 of FIG. 5 also is shownwith a mounting block 75 for the pressure regulator valve 76. Thefunction of the pressure regulator will be described in greater detailbelow. The fluid reservoir 58 can also be configured so as to have anindented area 60 in the base, optionally covered with a partial lid 61.The lid 61 provides a fluid tight cover over the indented area exceptfor a slit 59 which is open between the indented area 60 and theinterior of the reservoir in an area near the prisms 69, 74. In this waythe fluid opening leading to the reservoir outlet channel is locatednear the prisms and the prisms will most accurately reflect the fluidlevel available to the feedblock and thus the pump. This is seen in theembodiment of FIG. 5B. Heat exchange fluid enters the fluid reservoir 58from the inlet hole 56, collects in the reservoir and then flows intothe reservoir outlet channel 62. The reservoir outlet is at the base ofthe fluid reservoir 58 and is fluidly connected to an inlet 87 andinflow channel 86 of the feedblock section. This may be accomplished bythe snug fitting of an outlet collar 66 at the outlet channel 62 fromthe reservoir over a cylindrical protrusion 68 of the feedblock sectioninlet.

[0078] Referring to FIGS. 8, 5 and 5A, the feedblock section 80 has acentral chamber 90 which houses a priming valve 84 that directs fluidflow, an inlet 87 and corresponding inlet channel 86 from the reservoirand a fill port 18 and filling channel 88 from an external fluid sourcewhich both lead into the central chamber, an outflow channel leading 92from the central chamber to an outlet 93 which is directed to the pump,a flexible membrane 96 covering the central chamber, an optionalpressure regulator chamber 198 adjacent to an optional sensing chamber224 (having a diaphragm 204 and push rod 210) which communicates withthe pressure regulator valve when present, an optional pressure damper(not shown), an outlet channel 219 leading from the sensing chamber ordamper to a fluid coupling outlet means 149 in the feedblock section forfluidly connecting the bulkhead to the catheter fluid supply line 150,an inlet 95 and channel 196 which connects the pump to the sensingchamber or damper, and a flow-through channel 221 having a fluidcoupling inlet means 159 for fluidly connecting the catheter fluidreturn line 158 to the bulkhead and an outlet 97 which leads to the pumpsection and then to the external heat exchanger. The priming valve 84can be any suitable mechanism and is illustrated in the embodiment ofFIGS. 8, 5 and 5A as a spool valve.

[0079] Referring to FIGS. 10, 6 and 6A, the reservoir section 340 has aninlet hole 56 leading from the external heat exchanger 20 and an outletchannel 362 leading to the pump section 300, a fluid reservoir 358 forstorage of heat exchange fluid, a fluid level detector 369 formonitoring the level of heat exchange fluid within the fluid reservoir,a reservoir cover plate 353 that serves to retain fluid within thereservoir. The cover plate 353 seals the reservoir but is fitted with aone or more vent holes 55 into which are positioned a correspondingnumber of hydrophobic gas permeable vents 354 for releasing aircontained within the fluid reservoir. The reservoir section 340 also hasa fill port 318 connected to an external fluid source, and a pressuredamper, which comprises a pressure dampening chamber 230 filled with acompressible material 232. The reservoir section is fitted with a collar371 that couples the dampening chamber to the pump section.

[0080] The pressure of fluid flowing from the bulkhead to the catheterthrough fluid supply line 150, can be controlled in numerous ways. Inthe embodiment of FIG. 3 the pressure is controlled by a pressureregulator valve. However, a pressure regulator valve and the chambersthat operate with it are optional features and may be replaced by aconstant current system and a pressure damper, which is illustrated inFIG. 18.

[0081] In the embodiment of the invention having a pressure regulatorvalve, the fluid supply system is configured to have a reservoirsection, a feedblock section and a pump section, where the pressureregulator is contained within the feedblock section. It is understoodhowever, that the pressure regulator can be located in another portionof the bulkhead, for example as part of the pump or reservoir section,and still serve the same function. The pressure regulator comprises thepressure regulator valve that controls the pressure of the fluid flowfrom the feedblock section to the catheter mounted in the reservoirsection. The pressure regulator also comprises a pressure regulatorchamber (having a counter spring and counter spring block) adjacent to asensing chamber (having a diaphragm and push rod) which communicateswith the pressure regulator valve. Both the pressure regulator chamberand the sensing chamber are housed in the feedblock section. Thefeedblock section also has an outlet channel leading from the sensingchamber to an outlet in the feedblock section which leads to thecatheter and an inlet and inlet channel which connects the pump to thesensing chamber. One embodiment of the pressure regulator is shown inthe embodiments of FIGS. 5 and 5A, where the reservoir section 40,feedblock section 80 and pump section 100 are shown as being coupledtogether, and the pressure regulator comprises the pressure regulatorvalve 76, a pressure regulator chamber 198 (with counter spring 222 andcounter spring block 220) adjacent to a sensing chamber 224 (with adiaphragm 204 and push rod 210) which communicates with the pressureregulator valve. An outlet channel 219 on the feedblock section leadsfrom the sensing chamber to a fluid coupling outlet means 149 in thefeedblock section and serves to fluidly connect the bulkhead to catheterfluid supply line 150, while an inlet 95 and inlet channel 196 connectsthe pump to the sensing chamber.

[0082] The pump head can be any type such as is well known in the art,for example, a vane pump, a diaphragm pump, a peristaltic pump, animpeller pump, a gear pump and so forth. A preferred embodiment utilizesa cardioid vane pump, as shown in FIGS. 5 and 9. The pump section 100has a quasi-cardioid shaped cavity 104, into which is positioned a pumphead 140 that comprises a rotor 106, a vane 110 for moving fluid from aninlet 113 and inlet channel 112 to an outlet channel 114 and outlet 115,a wheel assembly for coupling to the motor and to facilitate movement ofthe pump head, for example a plurality of wheels 134, 136, and 138, anda flow-through channel 143 having an inlet 141 that leads from thefeedblock section 80 and an outlet hole 57 which leads to the externalheat exchanger 20. Referring to the embodiment shown in FIG. 6, the pumpsection 300 has the same shaped cavity 104 and pump head parts asdescribed for the embodiment of FIG. 5. The vane 110 moves fluid frominlet 113 and inlet channel 112 to the pump outlet channel 314. The pumpsection 300 also has a flow-through channel 343 having a fluid couplinginlet means 159 that leads from the catheter and an outlet hole 57 whichleads to the external heat exchanger 20. The pump outlet channel 314 isindependently in fluid communication with a pressure dampening chamber230. Outlet channel 314 is also configured with a fluid coupling outletmeans 149 for fluidly connecting the bulkhead to the catheter. Fluidmoving along this pathway encounters an opening 250 that exposes thefluid to the compressible material 232 within the dampening chamber. Thepump is able to pump fluid through the system at pressure in excess of35 psi. More critical to the invention, the pump is able to rapidlyachieve and maintain a predetermined pressure, for example 40 psi.

[0083] In the embodiment of FIGS. 3 and 7-9, the reservoir section 40 isshown as being coupled to the feedblock section 80 which in turn isshown as being coupled to the pump section 100; however, at least two ofthese sections can be housed together in one unit These sections can bereadily coupled as follows. The reservoir section 40 has two collars:outlet collar 66 and pressure regulator collar 67. These fit tightlyover two collars of slightly smaller size positioned on the feedblocksection, the inlet collar 85 and sensing chamber collar 225. Thefeedblock section has three additional collars: outlet collar 81, inletcollar 83 and outlet collar 89, around which are positioned O-rings 228.Collar 81 fits snugly with inlet 141, collar 83 fits snugly with outlet115 and collar 89 fits snugly with inlet 113. In the embodiment of FIGS.4 and 10, the reservoir section 340 is readily coupled to the pumpsection 300 by means of a collar 371 on the reservoir section that fitsinto a matching sleeve on the pump section 300, and an outlet channel362 that fits in the bottom of an L-shaped channel on the pump section.Any of the aforementioned sections in FIGS. 3 and 4 may further besecured with appropriate adhesive if desired.

[0084] The reservoir section can be provided with a means to monitor theamount of heat exchange fluid that is in the system, more specificallyan optical means for detecting the level of fluid contained within thefluid reservoir. Since the heat exchange fluid is a biocompatible fluidand the volume of the external source is about 250 ml, it is notexpected that fluid leakage into the patient will be problematic.However, the heat exchange fluid supply system of the invention isdesigned to detect the level of the fluid in the system so that awarning or other measure can be instituted if the system becomesunacceptably low.

[0085] Accordingly, in one aspect of the invention, the reservoirsection is provided with a means to detect the fluid level in thereservoir and comprises at least one prism mounted within the reservoirsection adjacent the inside of a relatively transparent window or wallportion in the reservoir, and at least one optical beam source and atleast one optical beam sensor mounted on the reusable master controlunit adjacent the outside of the window.

[0086] In one embodiment, the fluid level detector comprises a prismmounted in the reservoir, a light beam source and a light beam sensor.The prism has a diffraction surface and the light beam source directs alight beam against that surface. The prism is configured so that whenthe diffraction surface is in contact with air, the light beam isreflected to impinge on the light beam sensor and the sensor generates asignal. Likewise, when the diffraction surface is in contact with fluid,the light beam does not reflect to the sensor and the sensor does notgenerate a signal.

[0087] In operation, a light beam is directed through the reservoirsection and against the prism at a particular point along its angledlength. The sensor is located to detect the presence or absence of areflected beam. As long as the fluid reservoir remains full and thefluid level is at a pre-determined elevation above the point ofimpingement of the light beam, the diffraction surface of the prism atthat point is in contact with the fluid. Therefore, the light beamdirected at the prism travels through the prism and, upon reaching thediffraction surface, is reflected such that the sensor does not observea reflected beam. If the fluid falls below the pre-determined elevation,the diffraction surface of the prism at the point where the beamimpinges on it will no longer be in contact with the fluid and will bein contact with air instead. Air has a different index of refractionthan the index of refraction of the fluid. Accordingly, upon reachingthe diffraction surface, the reflected beam will no longer reflect outto the same point, and is reflected in such a manner that it impingesupon the sensor, which will then observe a reflected beam.

[0088] In a preferred embodiment, two prisms, each having acorresponding beam source and beam, are utilized. Each prism will have acorresponding beam source and sensor mounted on the reusable mastercontrol unit at a location adjacent to the prism. For example, FIG. 2illustrates placement of an optical beam source 166 and optical beamsensor 167 for the first prism 72 in the bulkhead design of FIG. 3. Anadjacent beam source and sensor would also be provided for the secondprism 74, if present. For the bulkhead design of FIG. 4, the beamsource(s) and sensor(s) would be position on the control unit 186 at alocation underneath the fluid level detector 369. The secondprism/source/sensor is redundant and functions to monitor the same fluidlevel as the first prism but operates as a safety mechanism in the eventhe first prism/source/sensor fails to function properly. Alternatively,one of the prisms may also have a “high level” sensing system that canbe used to signal the control unit when the fluid in the reservoirreaches a certain high level. This is useful, for example, when thevalved-priming system is used and detection of a high or full level isneeded to determine when to activate the valve to stop the primingsequence.

[0089] Referring to FIG. 7, a relatively transparent bulkhead materialor a relatively transparent window 70 configured in the bulkhead allowsfor optical observation of the fluid level in the fluid reservoir 58through the end of the reservoir section 40. First and second prisms 72,74 are mounted at the end of the fluid reservoir near the inlet hole 56.In the embodiment of FIG. 9, first and second prisms 372, 374 aremounted within the fluid reservoir near the pressure dampening chamber230. These prisms have a diffraction surface and may be machinedseparated and then affixed within the reservoir section or they may bemachined as part of the section, and are made of a material such aspolycarbonate. Although only one prism is needed for the fluid leveldetection method to function, it may be desirable to include a secondredundant prism as described above.

[0090] If desired, both high level and low level sensors can be employedon each prism. The sensors will generate a signal indicating that eitherthere is or is not fluid at the level of the optical beam. If theoptical beam source and sensor are positioned or the optical beam isdirected near the top of the tank, the indication that the fluid hasreached that level will trigger the appropriate response from thecontrol system, for example to terminate a fill sequence. On the otherhand, if the sensor is positioned or optical beam directed to sense thefluid level on the bottom of the tank, then the fluid level detector isconfigured to detect a low fluid level and can generates a signalrepresenting such low level. The cassette can then be configured torespond to this signal indicative of a low level of fluid in thereservoir. For example, the pump head can be designed to be responsiveto this signal such that the pump head stops pumping when a low fluidlevel is detected, so that air will not be pumped into the heat exchangecatheter.

[0091] In a preferred embodiment of the invention, the reservoir sectionis provided with a means to detect when the fluid reservoir is too low.In operation, the optical beam source is turned on to produce an opticalbeam that is directed towards the bottom of the prism and is reflectedback to the optical beam sensor. Typically, this source would beginoperation after the reservoir had started to fill with fluid. Thus,fluid would be in the reservoir and so the sensor will not observe areflected light beam. As long as this is the case, the pump willcontinue to operate, moving fluid through the cassette and catheter.However, if the fluid level drops below the level of the optical beam,the sensor then will observe a reflected light beam, which will triggerthe pump to cease operation and the system to shut down.

[0092] In the embodiment of the invention that involves a valved-primingsequence, the optical beam source is turned on to produce an opticalbeam that is directed towards the top of the prism and is reflected backto the optical beam sensor. As long as the sensor observes a reflectedlight beam, the fill operation of the cassette continues to run. As thefluid level rises, at some point it reaches a level such that theoptical beam is deflected and no longer reflects back to the sensor.When the sensor no longer observes a reflected light beam, the filloperation of the cassette ceases.

[0093] This is illustrated by referring to FIGS. 8, 11A and 11B, wherethe bulkhead is shown as further comprising a chamber 90 that houses avalve 84. The chamber has a first chamber inlet 18 that is in fluidcommunication with the external fluid source 15, a second chamber inlet87 in fluid communication with the reservoir outlet 62, and a chamberoutlet 93 in fluid communication with the pump inlet 113. The valve isdesigned to have a first position whereby the first chamber inlet isopen, the second chamber inlet is closed and fluid flows from theexternal fluid source to the pump inlet. In the second position of thevalve, the first chamber inlet is closed, the second chamber inlet isopen and fluid flows from the reservoir outlet to the pump inlet. Inthis embodiment, the fluid level detector is configured to detect a lowfluid level and a high fluid level, and the detector generates a firstsignal representing the low level and a second signal representing thehigh level. Initially, the valve is in its first position and ismaintained in this first position in response to the first signalthereby allowing fluid to enter reservoir until it reaches a high level,at which point the detector generates a second signal, and the valve isactuated to its second position.

[0094]FIGS. 5 and 6 also provide another view of the three hydrophobicgas permeable vents 54 located in the top of the reservoir section 40and 340, and positioned over the fluid reservoir 58 and 358. These ventsserve to purge air from the fluid supply by allowing gas such as air toescape, but will not vent fluid. In this way, as the fluid reservoirfills up, the air in the reservoir can be vented to the atmosphere,while not permitting any heat exchange fluid to escape. In addition thepore size on the vents is small enough to prevent the entrance of anycontaminants such as microbes, thus maintaining the sterility of thefluid that is being circulated through the catheter in the patient'sbody.

[0095] One embodiment of the invention pertains to a method forproviding a temperature regulated source of heat exchange fluid for heatexchange catheters, comprising the steps of: providing a circuitcomprising an external heat exchanger, a pump, a heat exchange catheter,and air vents, where the external heat exchanger, pump and heat exchangecatheter are in fluid communication such that fluid pumped by the pumpis circulated through the heat exchange catheter and the external heatexchanger, and the air vents allow passage of gas in and out of thecircuit through the vents but do not allow passage of liquid in and outof the circuit though the air vents; providing a heat generating orremoving unit in heat exchange relationship with the external heatexchanger, providing an external fluid source in fluid communicationwith the circuit; circulating heat exchange fluid from the externalsource through the circuit by means of pumping with the pump whilesimultaneously venting any gas contained in the circuit out through theair vents; and controlling the temperature of the heat exchanger fluidin the circuit by controlling the temperature of the heat generating orremoving unit.

[0096] This method may also include the step of providing a valvebetween the external fluid source and the circuit, where the valve hasan open position which permits the flow of heat exchange fluid from theexternal fluid source into the circuit and a closed position whichprevents the flow of heat exchange fluid from the external fluid sourceto the circuit. The method may also include use of a level sensor withinthe circuit to sense when the fluid level in the circuit is full, andwhere the level sensor generates a signal in response to the full fluidlevel. In combination with the valve, this method contemplates initiallymaintaining the valve in its open position until the sensor senses thatthe fluid level in the circuit is at an adequately full level andoperating the valve into the closed position in response to such signal.

[0097] The method of providing a temperature regulated source of heatexchange fluid can also include the step of controlling the pressure ofthe fluid as the fluid is circulated through the circuit. This pressurecontrol can be a pressure regulator in fluid communication with thecircuit, for example a pressure damping mechanism. This pressure controlcan also be achieved by using a pump that is operated by an electricmotor and maintaining a predetermined current to the electric motor.

[0098] Referring to FIGS. 19A and 19B, one method of supplying heatexchange fluid to an intravascular heat exchange catheter is illustratedby fluid flow pathway, each pathway illustrating a different embodimentof the cassette of the invention. In both embodiments, fluid flows fromthe pump to the heat exchange catheter. The fluid returns from thecatheter, passes through the external heat exchanger, and then enters afluid reservoir. From the reservoir, the fluid moves to the pump, andthe cycle repeats for the desired duration. An optional pressureregulator can be position in the fluid path moving from the pump to thecatheter. Fluid is provided from an external fluid source, which in theembodiment of FIG. 19A enters the priming valve, and in the embodimentof FIG. 19B enters the pump head.

[0099] Examples of these methods and the respective fluid pathways arefurther understood by reference to FIGS. 5A and 6A. In general, thismethod comprises the steps of: (a) providing power to operate a pumphead; (b) transferring fluid from an external fluid source to a chamber,(c) pumping fluid from the chamber into a pump cavity; (d) pumping fluidfrom the pump cavity to the catheter, (e) pumping fluid from thecatheter to a external heat exchanger which is positioned in heattransfer relationship with a heat generating or removing unit; (f)pumping fluid from the external heat exchanger to a heat exchange fluidreservoir, (g) pumping fluid from the heat exchange fluid reservoir intothe pump cavity; and (h) repeating steps (d) through (g) for theduration of operation of the catheter. Preferably a step for measuringthe fluid level in the heat exchange fluid reservoir is included. Suchstep can be used to insure that the reservoir remains full. Such stepcan also comprise using an optical fluid level detector to determine thefluid level, where step (h) begins when the reservoir is filled tocapacity and step (b) ceases when step (h) begins. The method forsupplying heat exchange fluid to a catheter using the embodiment of FIG.6A uses a passive-priming mechanism, while the embodiment of FIG. 5Auses a unique valved-priming mechanism, which is described in detailbelow. In the priming mechanism shown in FIG. 5A, the fluid levelmeasuring step may also comprise using an optical fluid level detectorto determine the fluid level, where step (g) begins when the reservoiris filled to capacity and step (b) ceases when step (g) begins.

[0100] Referring to the bulkhead embodiment of FIG. 6A and the flowdiagram of FIG. 19A, a method for supplying heat exchange fluid to anintravascular heat exchange catheter comprises the steps of: (a)transferring fluid from an external fluid source 15 to a chamber, whichis the heat exchange fluid reservoir 358; (b) providing power to operatea pump head 140 (c) venting air from the heat exchange fluid reservoiras the air is displaced by the fluid from the external fluid source; (d)pumping fluid from the chamber through a pump cavity 104, to a heatexchange catheter 160, through an external heat exchanger 20 which ispositioned in heat transfer relationship with a-heat generating orremoving unit, and pumping the fluid and air displaced by thecirculating fluid from the external heat exchanger 20 to the heatexchange fluid reservoir 358; (e) venting the air displaced by thecirculating heat exchange fluid from the heat exchange fluid reservoir;(f) repeating steps (a) through (e) for the duration of operation of thecatheter.

[0101] More particularly, the embodiment of FIGS. 6 and 6A provides themechanism for passively priming the system with heat exchange fluid froman external source 15. The external fluid source is placed above thereservoir, and is connected by a fluid providing line 16 to thereservoir. The reservoir 358 has a fill port 318 from the fluidproviding line 16. Initially, with the catheter out of the patient'sbody, the pump is operated to draw heat transfer fluid from the externalfluid supply and circulate it through the system. The air that is in thesystem is vented through the hydrophobic air vents. When the pressure inthe system is equal to the head pressure from the external fluid source(this will happen at a level which depends on the pump pressure and theheight of the external fluid source above the reservoir) the system willessentially be in equilibrium and will cease drawing fluid from theexternal source. At this point the catheter and cassette system will beconsidered to be primed. The heat exchange catheter will generallythereafter be inserted into the patient, and as the system is operated,any fluid required to be added to the system to maintain the pressureequilibrium mentioned above will be drawn from the external source whichis in fluid communication with the reservoir through fluid providingline. Likewise, any buildup of pressure in the system due, for exampleto the heating and expanding of the system, will be relieved by fluidflowing back into the external fluid supply source 15. Because of theability of the system to react to minor expansions and contractions offluid supply, there is no need to monitor the high level of fluid, andonly redundant sensors of the low level need be incorporated into thecassette.

[0102] Referring now to the bulkhead embodiment of FIG. 5A and the flowdiagram of FIG. 19B, a method for supplying heat exchange fluid to anintravascular heat exchange catheter comprises the steps of: (a)automatically operating a valve to open a fluid pathway between anexternal fluid source 15 and a chamber 90 in the feedblock section of abulkhead; (b) transferring fluid from an external fluid source 15 tochamber 90; (c) operating pump head 140 to pump fluid from the chamber90 into a pump cavity 104, through heat exchange catheter 160, throughexternal heat exchanger 20 which is positioned in heat transferrelationship with a heat generating or removing unit and to exchangefluid reservoir 58; (c) venting all air displaced by the heat exchangefluid supplied to and circulated through the system; (d) continuingsteps (a) through (c) until the fluid reservoir is full and excess airis purged from the system; (e) when the fluid reservoir is full,automatically operating a valve to close fluid communication between anexternal fluid source 15 and chamber 90; (f) continuing steps (b) and(c) for the duration of operation of the catheter. More particularly,the embodiment of FIG. 5A, with its feedblock, provides the mechanismfor automatically commencing and ceasing priming the system with heatexchange fluid from an external source 15 and for circulating fluid tothe catheter 160 in a closed circuit. The external fluid source 15 has afluid providing line 16, and the catheter has a fluid supply line 150and a fluid return line 158. The external heat exchanger 20 has an inletorifice 36 and an outlet orifice 38. A heat exchange fluid reservoir 58is connected to the external heat exchanger outlet 38. Pump 140 ispositioned in a pump cavity 104, which is connected to fluid supply line150. A chamber 90 comprises a valve 84, a fill port 18 from the fluidproviding line 16, a fluid inlet 87 from the heat exchange fluidreservoir 58, and a fluid outlet 93 to the pump 140. The valve has afirst position (FIG. 11B) whereby the fill port 18 from the fluidproviding line 16 is open and the fluid inlet 87 from the heat exchangefluid reservoir 58 is closed, and a second position (FIG. 11A) wherebythe fill port 18 from the fluid providing line 16 is closed and thefluid inlet 87 from the heat exchange fluid reservoir 58 is open. Anoptical fluid level detector detects when the heat exchange fluidreservoir 58 is filled to capacity. When the reservoir is not filled tocapacity the valve is in its first position. When the reservoir isfilled to capacity, the optical fluid level detector operates to movethe valve to its second position.

[0103] As can be seen from FIG. 19C, the direction of the fluid flow andthe inclusion of many of the above described elements are optional, andmay be changed, omitted or substituted as is appropriate for the fluidsupply system desired. Any such changes, substitutions or omissions maybe made without departing from the invention as disclosed, whichinvention is circumscribed only as is established in the claims.

[0104] Referring to FIGS. 11A and 11B, the priming valve 84 ispositioned within a central chamber 90, which has two inflow channels,an inflow channel 86 from the fluid reservoir 58 and a filling channel88 from inlet port 18 from the external fluid source 15. The centralchamber 90 also has a outflow channel 92 leading to the pump section. Afilter (not shown) may be located between the reservoir and the centralchamber to catch any particulate matter that may be in the heat exchangefluid. The chamber is fitted with a guide disc 171 to support thepriming valve. The priming valve is operable to fill the closed fluidcircuit comprising the heat exchange catheter 160, the external heatexchanger 20 and the bulkhead 30. It may be configured to automaticallyprime the system.

[0105] The embodiment of the priming valve illustrated in FIGS. 11A and11B is a spool valve 84, which is comprised of a spool valve stem 94, acompressible spring 99 contained within a solid block 101, and aplurality of O-rings 91. The spool valve is operable between a firstposition (FIG. 11B) and a second position (FIG. 11A), and is controlledby a spool valve activation system 164 which is mounted on the reusablemaster control unit 186, as shown in FIG. 2. The spool valve activationsystem 164 comprises a flexible membrane 96, a push rod 98 and a linearactuator 102. The valve stem 94 is located so that its top end ispositioned immediately below the membrane 96, which can be a siliconmembrane reinforced by cloth which is deformable by a sufficient degreeto allow the valve stem to be depressed to travel between the twopositions illustrated in FIGS. 11A and 11B. A push rod 98 may depressthe valve stem 94 by pushing against the membrane 96 and thence againstthe top end of the valve stem to operate the valve. The push rod, notcontained in the cassette of this invention, may be manually triggered,or may be automatically controlled. The push rod 98 may act, for exampleby means of a linear actuator 102, which will serve to exert downwardpressure on the push rod, as in FIG. 11B or will be in a releasedposition, as in FIG. 11A such that no downward pressure is exerted onthe spool valve stem 94.

[0106] The invention also encompasses a method for automaticallycommencing and ceasing the priming of a heat exchange fluid supplysystem for supplying a heat exchange fluid from an external fluid source15 to an intravascular heat exchange catheter 160, using the meansdescribed above. This method comprises the steps of: (a) first providingpower to operate the pump, wherein the reservoir is not filled tocapacity and the valve is in its first position and the pump 140operates to pump fluid: (i) from the external fluid source 15 throughthe fluid providing line 16 into the fill port 18 of the chamber 90 andout of the fluid outlet 93 into the pump cavity 104; (ii) from the pumpcavity 104 to said fluid return line 158 to the catheter 160; (iii) fromthe catheter 160 through the fluid supply line 150 to the external heatexchanger inlet orifice 36; (iv) from the external heat exchanger outletorifice 38 to the heat exchange fluid reservoir 58; and (v) into theheat exchange fluid reservoir 58 to fill the reservoir, (b) then fillingthe reservoir to capacity; at which point (c) the optical fluid leveldetector operates to move the valve to its second position and the pump140 operates to pump fluid from the heat exchange fluid reservoir 58 tothe fluid inlet 87 of the chamber 90 and out of the fluid outlet 93 intothe pump cavity 104.

[0107] When the disposable cassette of the invention is first put intooperation, the cassette 10 is initially filled with heat exchange fluidand an external fluid source such as an IV bag of saline is attached tothe filling channel 88. In addition, the linear actuator 102 isactivated, and the spool valve stem 94 is in its first position (FIG.11B, the valve stem depressed and the valve in the auto-prep position),depressed sufficiently to allow fluid to flow from the IV bag into thecentral chamber 90. In particular, the filling channel 88 is open to theoutflow channel 92 and the inflow channel 86 is closed, which allows theheat exchange fluid to flow from the external fluid supply source 15into the chamber 90 and then onto the pump section 100.

[0108] When the pump head 140 is active, heat exchange fluid isinitially pumped from the external fluid source 15 in to the chamber 90,then through the catheter 160, returning to the bulkhead 30 and thenonto the external heat exchanger 20, and from there into the reservoir58, as would be the case where the system was initially primed. As partof this process, air is expelled through the hydrophobic vents and thereservoir begins to fill with heat exchange fluid. The fluid level inthe reservoir rises since fluid is unable to move through outlet channel62 and inflow channel 86, which is closed due to the position of thespool valve.

[0109] The reservoir section is provided with a means to detect when thefluid reservoir is full, as described above, whereby signals areprovided to the reusable master control unit that represent orcorrespond to the level of the heat exchange fluid in the reservoir.Using the data representing the fluid level, the reusable master controlunit adjusts the linear actuator so that the position of the spool valvechanges and the fluid flow path is altered. Thus when the fluid level inthe reservoir 58 rises to a sufficient level, a signal is sent to thereusable master control unit to deactivate the linear actuator 102 sothat it moves to a released position and thus withdrawing the push rod98, resulting in the spool valve stem 94 being in its second position(FIG. 11A, the valve stem relaxed and the valve in the normal operatingposition). In this second position, the inflow channel 86 is open to theoutflow channel 92 and the filling channel 88 to the external fluidsource is closed. Thus, fluid from the now full reservoir is directedfrom inflow channel 86 to outflow channel 92 and then onto the pumpsection, while fluid flow from the external fluid source is diminishedor ceases entirely.

[0110] The valve is biased into the up position, that is the positionthat seals the filling channel 88, and opens the inflow channel 86. In apreferred embodiment the pump would continue to run for a period of timeafter the level sensor indicated that the system was full to ensure thatany air bubbles in the catheter or the external heat exchanger or thebulkhead would be expelled into the reservoir 58 where they could ventto the atmosphere. Since the fluid is being drawn from the bottom of thereservoir through reservoir outlet channel 62, and air moves up towardsthe top of the reservoir where the hydrophobic vents are located, thisacts to purge air from the system. Therefore, it is important to realizethat the spool valve may also have a third position that is anintermediate position from its first and second positions describedabove. In this manner, heat exchange fluid may enter the central chamber90 from either the reservoir or the external fluid source, or bothsimultaneously if the valve stem 94 is opened to this intermediateposition. So, for example, in an embodiment of the intention thatutilizes the pump in a first, intermediate and then second position,fluid would enter the pump solely from the external fluid source 15(first position, FIG. 11B), then fluid would enter the pump in part fromthe external fluid source 15 and in part from the reservoir 58(intermediate position) and finally fluid would enter the pump solelyfrom the reservoir 58 (second position, FIG. 11A).

[0111] The method for automatically commencing and ceasing the primingcan further comprises continuously supplying the heat exchange fluidfrom the pump to the catheter 160, by repeating steps (a)(ii) to (a)(v)and step (c)(i) for the duration of operation of the catheter, which canbe to 72 hours.

[0112] The pump section is readily adapted for use with the reservoirsection 40 and feedblock section 80 of the cassette of FIG. 3 or thereservoir section 340 of the cassette of FIG. 4 and is configured toallow for pumping of heat exchange fluid at a constant pressure. In thisembodiment of the invention, the pumping mechanism creates rapid flow ina heat exchange fluid supply system for supplying a heat exchange fluidto an intravascular heat exchange catheter, and comprises a cavityhaving a quasi-cardioid shape, an inlet to the cavity, an outlet fromthe cavity, a pump head comprising a rotor having a central groove, anda vane slidably mounted in the groove and impinging on the edge of thecavity.

[0113] This is illustrated in FIGS. 9 and 12A, where the pump section100 contains a cavity 104 of quasi-cardioid shape and the pump head 140.The pump head has a rotor 106 which is circular and rotates within thecavity 104, and has a central groove 108 across the entire center of therotor. A vane 110 is slidably mounted in the groove and impinges on theedge of the cavity 104. As the rotor 106 rotates around its center, thevane 110 moves freely, sliding back and forth within the groove 108,with the ends of the vane 120, 122 being continuously in contact withthe edge of the cavity 104.

[0114] A fluid inlet channel 112 leads from the feedblock section 80 andopens into the cavity 104 just beyond the edge of the rotor 106. A fluidoutlet channel 114 opens into the cavity 104 on the opposite side of therotor 106 and leads to the feedblock section 80. As the rotor 106rotates, the vane 120 is in continuous contact with the cavity wall 123in relatively fluid tight contact. Fluid enters into the cavity 104 fromthe inlet channel 112 and is contained in the cavity between the cavitywall 123, the rotor wall 124 and the vane 110. As the rotor 106 rotatesthe vane also moves. This causes the fluid path to increase in area asit is filled with heat exchange fluid from the inlet channel 112, andthen decrease in area as the vane pushes the heat exchange fluid throughoutlet channel 114. The rotor wall 124 is in relatively fluid tightcontact with the wall of the cavity along arc 116 and therefore fluidcannot travel directly from the inlet channel 112 to the outlet channel114 of the pump. As the rotor rotates, fluid is pumped from the inletchannel 112 around the quasi-cardioid shaped cavity and pushed by thevane out the outlet 20 channel 114. The configuration of the fluid pathcan be likened to a “crescent” shape, as can be seen in FIG. 12A.

[0115] The pump is designed to rotate within the range of 200-1000 rpmand to function for up to 72 hours. The choice of materials should beselected to accommodate these needs, and suitable materials aredescribed below. It is an additional advantage of the curved edges 120and 122 on the vane that the point of contact between the vane edges andthe cavity wall 123 changes constantly through the rotation of the rotorand thus avoids a single wear point on the edges of the vane. Thisallows the vane to rub against the wall of the cavity for as long as 72hours and yet retain a relatively fluid tight contact between the edgesof the vane and the wall of the cavity. In a preferred embodiment, thevane is designed to fit in the cavity 104 at room temperature with aslight clearance, for example 0.005 inches. This clearance is one meansof accommodating the transient and steady state thermal changes thatoccur during operation and allows for expansion of the vane due to anincrease in temperature during operation. In this manner, at thetemperatures that are encountered during normal operation, the ends ofthe vane 120, 122 will maintain adequate contact with the wall 123 ofthe cavity 104 for pumping.

[0116] There are numerous other vane designs that also accommodatethermal changes so that the vane remains in continuous contact with thewall of the cavity and is able to move smoothly within the cavity. FIGS.20A, 20B and 20C are side views of examples of such designs. In FIG.20A, the vane 181 is configured with cut-out sections 173, 175, whichallow for expansion or contraction of the vane during operation. In FIG.20B, the vane 182 is configured with a center section 177 made of acompressible material to accommodate expansion or contraction of the endportions 179 during operation. In FIG. 20C, the vane 183 is configuredwith a center spring 211 to bias the end portions 209 outward duringoperation to contact the wall of the cavity regardless of thetemperature of the vane.

[0117] One embodiment of the invention relates to the geometry of thequasi-cardioid shaped cavity 104 having a circumference and an inlet 112and an outlet 114 thereto, that is part of the pumping mechanism of thedisposable cassette 10, which cassette is also comprised of a pump head140 comprising a rotor 106 having a central groove 108 and a diameter“D”, and a vane 110 having length “L” slidably mounted in the groove andimpinging on the edge of the cavity. As shown in FIG. 12B, thecircumference of the cavity has four arcs, where the radius “R” or eacharc has its center at the center of the rotor 106 and is measured to thecavity wall 123.

[0118] The four arcs 116, 117, 118 and 119 are as follows: (a) a firstarc defined as 330° to 30° and having a radius R₁, (b) a second arcdefined as 150° to 210° and having a radius R₂, (b) a third arc definedas 30° to 150° and having a radius R₃, and (d) a fourth arc defined as210° to 330° and having a radius R₄. These measurements are based uponthe center of the rotor and 0° is identified with the point midwaybetween the inlet and the outlet of the cavity, i.e., the line projectedfrom the center of the rotor 106 and the point on the cavity wall thatis midway between the inlet channel 112 and the outlet channel 114 isdesignated as the base line, from which 0-360° angles are measured, in aclockwise fashion. The four radii are defined as follows:

R ₁ =D/2

R ₂ =L−(D/2)

R ₃=(D/2)+{[(L−D)/2]·[cos(1.5θ+135)]}

R ₄=(D/2)+{[(L−D)/2]·[cos(1.5θ−315)]}

[0119] Therefore, arc 116 (330° to 30°) is circular and thus has aconstant radius, designated R₁; arc 117 (30° to 150°) is not circularsince its radius changes as the angle of rotation (designated “θ”)increases from 30° to 150°, and is designated R₃; arc 118 (150° to 210°)is also circular and thus also has a constant radius, designated R₂; andarc 119 (210° to 330°) is not circular since its radius changes as theangle of rotation decreases from 210° to 330°, and is designated R₄.These calculations are somewhat approximate because the vane has width,and the end of the vane also has a radius (i.e. is curved) and the exactcontact point between the vane and the wall of the cavity variesslightly with the rotation of the rotor. Since both ends of the vanehave the same radius of curvature, this is equal on each side, and theexact shape of the cardioid cavity can be adjusted to compensate forthis slight variance and still maintain contact at all points betweenthe vane and the cavity wall.

[0120] Turning to FIG. 13, the rotor 106 of the pump head is made of arigid and durable material with adequate lubricity to sustain a longperiod of close contact with the cavity wall 123 while rotating withoutundue wear. The rotor 106 may be made of, for example, polyvinylidenefluoride, and the vane 120 may be made of a material such as highdensity polyethylene. The rotor is mounted on a shaft 128 by means of apin 129 and has a seal 130 and a bearing 132 separated by an optionalspacer 131, provided in a manner known to those of skill in the art ofrotating shafts mounted in fluid-tight arrangement.

[0121] The shaft 128 protrudes below the rotor 106 and is fitted withthree wheels 134, 136 and 138 which cooperate with a pump drivemechanism 184 housed in the reusable master control unit 186, whichimparts rotational motion to the shaft and thence to the rotor. The topmost wheel 134 is a smooth alignment wheel, the middle wheel 136 is atoothed drive wheel, and the bottom most wheel 138 is another smoothalignment wheel. The drive wheel 136 can be constructed, for example, ofa plastic material such as nylon or polyurethane. The alignment wheels134 and 138 can be constructed, for example, of a polycarbonatematerial. These three wheels cooperate with a plurality of wheels on thereusable master control unit 186, two of which are depicted in FIG. 2 asguide wheels 190 and 192. A toothed motor wheel 188 is driven by thepump drive mechanism 184, and is shown in FIGS. 14 and 15, which depictplacement of the pump wheels 134, 136 and 138 within the control unit186. FIGS. 2 and 14 also shows placement of the gear shield 19, whichcovers the opening in the control unit 186 once the cassette 10 ispositioned in place.

[0122] When the cassette 10 is inserted into the reusable master controlunit 186, the toothed drive wheel 136 engages the toothed portion 189 ofmotor wheel 188. The drive wheel 136 and motor wheel 188 are held insnug juxtaposition by contact between guide wheels 190, 192 andalignment wheels 134, 138, respectively. As can be seen in FIG. 15, theguide wheels have a larger diameter top 191 and bottom 193 section, witha small diameter middle section 195. This allows the top 191 to fitsnugly against alignment wheel 134 and the bottom 193 to fit snuglyagainst alignment wheel 138, while at the same time the middle section195 will not come in to contact with the toothed drive wheel 136. Theguide wheels can be machined as a single spool-shaped unit or the top,middle and bottom sections can be separate pieces that are permanentlyaffixed together. The toothed motor wheel can also be designed to have aslightly larger top section 207 that fits snugly against alignment wheel134 and/or a slightly larger bottom section 208 that fits snugly againstalignment wheel 138. Preferably the motor wheel makes contact with atleast one of the smooth alignment wheels.

[0123] The positioning of the alignment and guide wheels causes theteeth of motor wheel 188 and drive wheel 136 to engage at theappropriate distance so that the teeth are not forced tightly together.The diameter of the smooth alignment wheels 134, 138 will beapproximately the pitch diameter of the drive wheel 136 to provideproper positioning of the drive teeth. Similarly, the diameter of thetop and bottom sections, 207, 208, of the motor wheel 188 will beapproximately the pitch diameter of the toothed portion 189 of the motorwheel 188. This is advantageous in imparting smooth rotation motionwithout imparting side forces to the drive shaft, or causing frictionbetween the teeth by virtue of their being jammed together.

[0124] The diametral pitch of the drive wheel 136 and the motor wheel188 are the same; however they will typically have different diameters.For example, a suitable diametral pitch is 48 (48 teeth per inch indiameter), which has been found to provide adequate strength withminimal noise during operation. A typical drive wheel 136 will have apitch diameter of 1″, while the corresponding motor wheel 189 will havea pitch diameter of about ⅜″.

[0125] The pump is designed to operate for significant periods of time,for example in excess of 72 hours, at fairly high rotational speeds, forexample approximately 800 rpm, and to operate to pump fluids oftemperature that vary between approximately 0° C. and 45° C. It isdesirable that the heat exchange catheter is supplied with fluid at arelatively constant pressure at the inlet to the catheter, for exampleabout 40-46 psi, but wear and temperature variations may affect theoutput pressure of the pump. In the embodiment which includes thepressure regulator, the pump is designed to have an output pressureslightly higher than the optimal pressure for the heat exchangecatheter, for example 42-48 psi, and the pressure is regulated down tothe desirable pressure of 40-46 psi. If the output pressure of the pumpvaries, the pressure regulator can be incorporated into the disposableheat exchange supply cassette 10 to ensure that the heat exchangecatheter is provided heat transfer fluid at a relatively constantpressure. The pressure regulator can be, for example, a pressureregulator valve or a pressure damper used with a constant current supplyin the disposable heat exchange supply cassette 310.

[0126] A preferred pressure regulator valve is described here, but itmay be readily perceived that one of ordinary skill may substitute anyappropriate pressure regulator valve for this function. In the preferredembodiment of the pressure regulator valve shown in FIG. 16, the outlet114 of the pump is fluidly connected to the inlet of the pressureregulator chamber 198 by means of channel 196. The pressure of the fluidat the pump output may vary somewhat depending on wear and fluidtemperature, and may be, for example, 45-54 psi.

[0127] A pressure regulator shaft 200 is mounted in the fluid reservoir58 through the mounting block 75. This may be in the form of a shaftwith screw threads mounted in a hole 194 in the block with mating screwthreads. A reference spring 202 is mounted between the shaft 200 and adiaphragm 204. The diaphragm may be a membrane, for example, a clothreinforced silicone membrane. The pressure on the reservoir side of thediaphragm is the pressure of the fluid in the reservoir 58, which byvirtue of the hydrophobic gas permeable vents 54 is essentiallyatmospheric pressure, plus the pressure applied by reference spring 202.The pressure of reference spring 202 may be adjusted by turning theshaft in the hole and thus tightening or loosening the spring againstthe diaphragm. A pressure block 206 is attached between the diaphragm204 and the reference screw 202 to apply distribute the pressure of thespring to the reservoir side of diaphragm 204.

[0128] On the other side of the diaphragm 204 a push rod 210 isattached. The push rod 210 extends through a throttle chamber 212. Thethrottle chamber 212 has a cloverleaf cross sectional configuration inthe form of a central throttle aperture 216 surrounded by four lobes214, as may best be seen in FIG. 17. The end of the push rod 210 distalof the diaphragm 204 extends to the end of the throttle chamber 212 tothrottle aperture 218. A counter spring block 220 is mounted across theface of the aperture 218 and is biased toward the aperture by meanscounter spring 222. This counter-spring block 220 may seal down againstthe open aperture 218 to create a fluid-tight seal between the sensingchamber 224 and the regulator chamber 198. Alternatively, if thepressure applied against the diaphragm by the spring 202 and thepressure in the reservoir 58 is sufficient to deform the diaphragminward toward the sensing chamber 224, the push rod 210 forces thecounter-spring block 220 away from the throttle aperture 218 and thusopens a throttle gap through which fluid may flow between the regulatorchamber 198 and the sensing chamber 224. Because the throttle gap isrelatively narrow, there is a pressure drop as fluid flows through thethrottle gap. In practice, the reference spring 202 is adjusted so thatthe pressure against the diaphragm 204 and thus against the push rod 210is about 43 psi. When the pressure in the regulator reservoir 198 isgreater than 43 psi, it forces the counter spring block 220 closer tothe throttle aperture 218 thus narrowing the throttle gap. Thisfunctions to automatically adjust the throttle gap so that the pressuredrop across the throttle gap is the same as the excess pressure betweenthe fluid in the regulator reservoir 198 and the pressure set by thereference spring 202 against the diaphragm 204, generally 43 psi. Thisacts to regulate the pressure of the fluid in the sensing chamber 224 to43 psi. The fluid exits the sensing chamber through outlet 220 andthence to fluid supply line 150 to the catheter. In this way fluid at arelatively constant pressure is supplied to the catheter. It may also beseen that such a pressure regulator may function to damp any pressurevariations, such as vibrations in the fluid line generated by the pump.For such uses, a regulator as described herein may be adequate. Otherpressure regulators, as are well known in the art, will also suffice forregulating pressure of the pumped fluid, including systems forcontrolling other flow characteristics such as dampening vibrations.

[0129] In operation, the rotor 106, including vane 110, is rotating at asufficiently constant rate to generate relatively constant pressure.However, due to the shape of the cavity 104, a variable pressure can beimparted to the fluid being moved by the vane, resulting in pressurefluctuations or uneven fluid flow in the fluid flowing from thefeedblock section 80 to the catheter through fluid supply line 150.These pressure fluctuations or uneven fluid flow may cause undesirablevibration of the catheter through which the fluid is flowing. In theembodiment described in FIG. 5, the pressure regulator serves toeliminate undesirable pressure fluctuations.

[0130] However, it may be desirable to eliminate the pressure regulatorvalve, pressure regulator chamber and sensing chamber from the cassettedesign. In that instance, another means of insuring constant pressureand providing for smooth fluid flow can be incorporated into thecassette design.

[0131] The pump drive mechanism 184 typically comprises an electricmotor and a power supply that provides the necessary current to run themotor. Constant current can be attained by directing the voltage fromthe power supply to an amplifier which adjusts and controls thefluctuating voltage input to provide a constant current output to themotor. With a constant current supplied to the electric motor that runsthe pump, the motor provides for constant torque to the pump head 140,which ultimately provides for constant pressure supplied to the catheter160.

[0132] Accordingly, in one embodiment of the disposable cassette of theinvention, the cassette comprises an external heat exchanger having aninlet and an outlet, a first fluid supply line in fluid communicationwith the heat exchanger inlet, a disposable pump head having a pumpinlet in fluid communication with the heat exchanger outlet and having apump outlet, a second fluid supply line in fluid communication with thepump outlet for receiving fluid pumped out of the pump outlet, and anoptional pressure regulator in fluid communication with the pump outletfor regulating the pressure of fluid pumped from the pump head. The pumphead is actuated by an electric motor that is controlled by an amplifiercontroller, where the amplifier controller supplies a constant currentto the pump head thereby causing the pump head to supply a relativelyconstant pressure to the fluid in the second fluid supply line.

[0133] In another embodiment of the invention, the cassette comprises:(a) an external heat exchanger comprising a structural member and acompliant member, where the compliant member is sealed to the structuralmember in a pattern that forms a flow channel between the compliantmember and the structural member, and where the flow channel has aninlet and an outlet; (b) a first fluid supply line in fluidcommunication with the flow channel inlet; (c) a bulkhead comprising areservoir and a disposable pump head, where the reservoir contains aninlet in fluid communication with the flow channel outlet, and furtherhas a fluid level detector for detecting the level of fluid within thereservoir, wherein the pump head is a cardioid vane pump head having aninlet and an outlet, and the pump head is actuated by an electric motor,where the pump inlet is in fluid communication with the reservoir outletand the electric motor is controlled by an amplifier controller, wherethe amplifier controller supplies a constant current to the pump headthereby causing the pump head to supply a relatively constant pressureto the fluid in the second fluid supply line; (d) a second fluid supplyline in fluid communication with the pump outlet for receiving fluidpumped out of the pump outlet; (e) an external fluid source in fluidcommunication with the reservoir, and (f) a pressure damper in fluidcommunication with the pump outlet.

[0134] One embodiment for providing smooth fluid flow is illustrated inFIG. 18, which is a cross-sectional view of a pressure damper, that maybe used in place of the pressure regulator components. In thisembodiment of the invention, a pressure damper is included in a heatexchange fluid supply system for supplying a heat exchange fluid to anintravascular heat exchange catheter where the heat exchange fluidsupply system has a reservoir section, a feedblock section and a pumpsection, wherein the pressure damper comprises a pressure dampeningchamber filled with a compressible material housed in the feedblocksection, adjacent to a flow-through channel having an inlet which leadsfrom the pump and an outlet which leads to the catheter. Thecompressible material is preferably air tight. Suitable examples includea block of foam, encapsulated foam such as polyethylene foam encased ina polyethylene film, foam enclosed within a sealed plastic pouch, foamcoated with or impregnated with plastic or silicone, gas encapsulatedwithin a flexible pouch such as a polyethylene balloon, and so forth.

[0135] Referring to FIG. 18, a pressure dampening chamber 230 ispositioned adjacent to and in fluid flow communication with the fluidflowing from the pump in the pump outlet channel 314 towards the outletchannel 319. As can be seen in FIG. 18, the dampening chamber need notbe positioned directly in the fluid flow path. The chamber must simplybe in a position such that it is in contact with fluid being pumped fromthe pump through channel 314. The chamber 230 is partially filled with acompressible material 232. As fluid contacts the compressible material232, the material compresses slightly and then returns to its originalconfiguration, and in doing so acts as a cushion to absorb minorpressure fluctuations uneveness of the fluid flow. This compressiblematerial movement thus has the effect of smoothening the fluid flow.

[0136] The external heat exchanger 20 is attached to the bulkhead 30 orbulkhead 330 by means of a mechanical seal formed when the external heatexchanger is attached over the bulkhead and a cover plate shown as coverplate 168 in FIG. 3 and as cover plate 368 in FIG. 4. The cover plate isattached over the external heat exchanger and attached to the bulkhead,trapping the extended attachment 48 of the external heat exchangerbetween the cover plate and the bulkhead. Referring to the embodiment ofFIG. 3, the cover plate is formed with a handle 170, a vent aperture 172that is located over and seal the periphery of the hydrophobic gaspermeable vents. 54 to allow any air present in the fluid reservoir 58to vent to the atmosphere. The cover plate is also formed with a primingvalve aperture 174 that provides access to the cover of the primingvalve 84, for example so that push rod 98 is able to contact theflexible membrane 96 and depress the valve stem 94 during the automaticpriming sequence described above. Located on the bottom of the coverplate 168 are two circular recessed areas (not shown), a first recess178 that fits over and seals the priming valve 84 and a second recess180, containing an O-ring 182 that fits over and seals cavity 104. Thebottom of the cover plate may have one or more straight recessed areasinto which a portion of the fluid lines such as lines 16, 150, 158 maybe positioned. The cover plate may be secured to the bulkhead by anysuitable means, for example by a plurality of suitably positionedhex-headed screws 176.

[0137] The cover plate is also configured to have one or more means forindicating to the user that the cassette is in the correct position foroperation. For example, the cover plate may have a slot that operates todepress a switch on the control unit to indicate proper placement.Similarly, the cover plate may have slots 199 and 201, withcorresponding depressions 203 and 205, which correspond to bearings onthe control unit. When the cassette is being positioned within thecontrol unit, the bearings will move along the slots 199 and 201 andonce the cassette is completely in place, the bearings will move intodepressions 203 and 205, with an audible click to inform the user thatplacement is complete.

[0138] Cover plates 168 and 368 are configured in a similar manner, withthe exception that cover plate 368 does not have a priming valveaperture 174 or first recess 178 since the embodiment of FIG. 4 does nothave a priming valve.

[0139] Referring back to FIGS. 1 and 2, the disposable fluid supplycassette 10 of the invention is shown as being attached to a heatexchange catheter 160, external fluid source 15 and positioned incooperation with a suitable reusable master control unit 186. Prior tocommencing treatment, the cassette is inserted into the reusable mastercontrol unit, the external fluid source is attached to the fill port andthe pump is automatically or passively primed and filled, after whichthe catheter is ready for insertion in the vasculature of the patient,for example in the inferior vena cava or the carotid artery. Chilled orwarmed biocompatible fluid such as saline, is pumped into the closedcircuit catheter, which exchanges heat directly with the patient'sblood. The control unit serves to automatically control the patient'stemperature. Once treatment with the catheter is complete, the catheteris removed from the patient and the cassette is removed from thereusable master control unit. Both the catheter and cassette are thendiscarded. The reusable master control unit, however, which never comesinto direct contact with the heat exchange fluid, is ready for immediateuse for treatment on other patients, along with a new cassette andcatheter and fresh external fluid source.

[0140] Each of the patents, publications, and other published documentsmentioned or referred to in this specification is herein incorporated byreference in its entirety.

[0141] While the present invention has been described with reference tothe specific embodiments thereof, it should be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particularsituation, material, composition of matter, process, process step orsteps, while remaining within the scope of the present invention.Accordingly, the scope of the invention should therefore be determinedwith reference to the appended claims, along with the full range ofequivalents to which those claims are entitled.

What is claimed is:
 1. A disposable cassette for supplying a heatexchange fluid to a heat exchange catheter, said cassette comprising: anexternal heat exchanger comprising a flow channel having an inlet and anoutlet; a first fluid supply line, said first fluid supply line in fluidcommunication with said flow channel inlet; a pump head contained in thedisposable fluid supply cassette, said pump head having a pump inlet anda pump outlet, said pump inlet in fluid communication with said externalheat exchanger flow channel outlet for pumping fluid from said flowchannel outlet; a second fluid supply line, said second fluid supplyline in fluid communication with said pump outlet for receiving fluidpumped out of said pump outlet; and a pressure regulator, said pressureregulator in fluid communication with said pump outlet for regulatingthe pressure of fluid pumped from said pump.
 2. The cassette of claim 1wherein said external heat exchanger comprises a structural member and acompliant member, said compliant member being sealed to said structuralmember in a pattern, said pattern forming a flow channel between saidcompliant member and said structural member.
 3. The cassette of claim 1wherein first and second fluid supply lines are connected through a heatexchange catheter thereby creating a fluid circuit including saidexternal heat exchanger, said pump, said first and second fluid lines,and said catheter.
 4. The cassette of claim 1 wherein said pressureregulator is a regulator valve.
 5. The cassette of claim 4 wherein saidpressure regulator further comprises a pressure regulator chamberadjacent to a sensing chamber which communicates with the pressureregulator valve.
 6. The cassette of claim 5 wherein said pressureregulator chamber comprises a counter spring and a counter spring block.7. The cassette of claim 5 wherein said sensing chamber comprises adiaphragm and a push rod.
 8. The cassette of claim 1 wherein saidpressure regulator is a pressure damper.
 9. The cassette of claim 8wherein said pressure damper is a compressible material.
 10. Thecassette of claim 9 wherein said compressible material is a block offoam.
 11. The cassette of claim 10 wherein said foam is enclosed with asealed plastic pouch.
 12. The cassette of claim 10 wherein said foam iscoated with plastic or silicone.
 13. The cassette of claim 9 whereinsaid compressible material is a gas encapsulated within a flexiblepouch.
 14. A heat exchange fluid supply system for a heat exchangecatheter, said system comprising: an external heat exchanger comprisinga structural member and a compliant member, said compliant member sealedto said structural member in a pattern, said pattern forming a flowchannel between said compliant member and said structural member; saidflow channel having an inlet and an outlet; a first fluid supply line,said first fluid supply line in fluid communication with said flowchannel inlet; a bulkhead, said bulkhead comprising a pump and areservoir, said reservoir having a reservoir inlet and a reservoiroutlet, said reservoir inlet in fluid communication with said externalheat exchanger flow channel outlet, said pump having a pump inlet and apump outlet, said pump inlet in fluid communication with said reservoiroutlet for pumping fluid from said reservoir outlet; a second fluidsupply line, said second fluid supply line in fluid communication withsaid pump outlet for receiving fluid pumped out of said pump outlet; andan external fluid source, said external fluid source in fluidcommunication with said bulkhead.
 15. The system of claim 14 whereinsaid reservoir further comprises at least one fluid level detector. 16.The system of claim 15 wherein said fluid level detector comprises atleast one prism mounted within the reservoir section, at least oneoptical beam source and at least one optical beam sensor, said sourceand sensor being mounted on a reusable master control unit adjacent tothe prism.
 17. The system of claim 15 wherein: said bulkhead furthercomprises a chamber comprising a valve, a first chamber inlet in fluidcommunication with the external fluid source, a second chamber inlet influid communication with the reservoir outlet, and a chamber outlet influid communication with the pump inlet; said valve having: a firstposition whereby the first chamber inlet is open, the second chamberinlet is closed and fluid flows from the external fluid source to thepump inlet; and a second position whereby the first chamber inlet isclosed, the second chamber inlet is open and fluid flows from thereservoir outlet to the pump inlet; and said fluid level detector isconfigured to detect a low fluid level and a high fluid level and saiddetector generates a first signal representing said low level and asecond signal representing said high level; and wherein initially thevalve is in its first position and is maintained in said first positionin response to said first signal thereby allowing fluid to enterreservoir until it reaches said high level and said level detectorgenerates said second signal, and said valve is actuated to its secondposition.
 18. The system of claim 15 wherein said fluid level detectoris configured to detect a low fluid level and generates a signalrepresenting said low level, and said pump is responsive to said signalsuch that said pump stops pumping when said low level is detected. 19.The system of claim 14 further comprising a pressure regulator, saidpressure regulator in fluid communication with said pump outlet forregulating the pressure of fluid pumped from said pump.
 20. The systemof claim 14 wherein said first and said second fluid supply line areconnected in a circuit through a heat exchange catheter.
 21. The systemof claim 15 wherein said at least one fluid level detector comprises: aprism mounted in said reservoir, said prism having a diffractionsurface; a light beam source; a light beam sensor; and wherein saidprism is configured so that when light beam is directed against saiddiffraction surface when said diffraction surface is in contact withair, said light beam is reflected to impinge on said light beam sensorand said sensor generates a signal, and when said diffraction surface isin contact with fluid, said light beam does not reflect to said lightbeam sensor and said sensor does not generate a signal.
 22. A disposablecassette for supplying heat exchange fluid to a heat exchange catheter,said cassette comprising: an external heat exchanger having an inlet andan outlet; a first fluid supply line, said first fluid supply line influid communication with said heat exchanger inlet; a disposable pumphead contained in the cassette, said pump head actuated by an electricmotor, said pump head having an inlet and an outlet, and said pump inletin fluid communication with said heat exchanger outlet; and a secondfluid supply line, said second fluid supply line in fluid communicationwith said pump outlet for receiving fluid pumped out of said pumpoutlet.
 23. The cassette of claim 22 wherein said electric motor iscontrolled by an amplifier controller, said amplifier controllersupplying a constant current to said pump head thereby causing said pumphead to supply a relatively constant pressure to said fluid in saidsecond fluid supply line.
 24. The cassette of claim 22 which furthercomprises a pressure regulator, said pressure regulator being in fluidcommunication with said pump outlet for regulating the pressure of fluidpumped from said pump.
 25. The cassette of claim 22 wherein said pumphead is a cardioid vane pump.
 26. The cassette of claim 25 wherein saidpump head comprises a rotor that is fitted with a vane for moving fluidfrom the pump, said rotor being positioned in a quasi-cardioid shapedcavity.
 27. The cassette of claim 26 wherein: (a) said cavity has acircumference, said rotor has a diameter “D”, and said vane has a length“L”; (b) the cavity circumference comprises: (i) a first arc defined as330° to 30° and having a radius R₁; (ii) a second arc defined as 150° to210° and having a radius R₂; (iii) a third arc defined as 30° to 150°and having a radius R₃; and (iv) a fourth arc defined as 210° to 330°and having a radius R₄; (c) wherein all measurements are based upon thecenter of the rotor and 0° is identified with the point midway betweenthe inlet and the outlet of the cavity; wherein the radii are definedas: R ₁ =D2 R ₂ =L−(D/2) R ₃=(D/2)+{[(L−D/2]·[cos(1.5θ+135)]}R₄=(D/2)+{[(L−D/2]·[cos(1.5θ−315)]}
 28. The cassette of claim 22 whereinsaid pump head is an impeller pump.
 29. The cassette of claim 22 whereinsaid pump head a gear pump.
 30. A method for providing a temperatureregulated source of heat exchange fluid for heat exchange catheters,comprising the steps of: providing a circuit comprising an external heatexchanger, a pump, a heat exchange catheter, and air vents, saidexternal heat exchanger, pump and heat exchange catheter in fluidcommunication such that fluid pumped by the pump is circulated throughsaid heat exchange catheter and said external heat exchanger, and saidair vents allow passage of gas in and out of said circuit through saidvents but do not allow passage of liquid in and out of said circuitthough said air vents; providing a heat generating or removing unit inheat exchange relationship with said external heat exchanger; providingan external fluid source in fluid communication with said circuit;circulating heat exchange fluid from said external source through saidcircuit by means of pumping with said pump while simultaneously ventingany gas contained in said circuit out through said air vents; andcontrolling the temperature of said heat exchanger fluid in said circuitby controlling the temperature of said heat generating or removing unit.31. The method of claim 30 further comprising the steps of: providing avalve between said external fluid source and said circuit, said valvehaving an open position which permits the flow of heat exchange fluidfrom said external fluid source into said circuit and a closed positionwhich prevents the flow of heat exchange fluid from said external fluidsource to said circuit; providing a level sensor within said circuit tosense when the fluid level in said circuit is fill, said level sensorgenerating a signal in response to said full fluid level; initiallymaintaining said valve in said open position until said sensor sensesthat the fluid level in said circuit is at an adequately full level; andoperating said valve into said closed position in response to saidsignal.
 32. The method of claim 30 further comprising the step ofcontrolling the pressure of said fluid as said fluid is circulatedthrough said circuit.
 33. The method of claim 32 wherein said pressurecontrol comprises a pressure regulator in fluid communication with saidcircuit.
 34. The method of claim 33 wherein said pressure regulator is apressure damping mechanism.
 35. The method of claim 32 wherein said pumpis operated by an electric motor, and said pressure is controlled bymaintaining a predetermined current to said electric motor.
 36. Acassette for supplying heat exchange fluid to a heat exchange catheter,said cassette comprising: an external heat exchanger comprising astructural member and a compliant member, said compliant member sealedto said structural member in a pattern, said pattern forming a flowchannel between said compliant member and said structural member; saidflow channel having an inlet and an outlet; a first fluid supply line,said first fluid supply line in fluid communication with said flowchannel inlet; a bulkhead, said bulkhead comprising a reservoir and adisposable pump head, said reservoir containing an inlet in fluidcommunication with said flow channel outlet, said reservoir furtherhaving a fluid level detector for detecting the level of fluid withinsaid reservoir, said pump head being a cardioid vane pump head, saidpump head actuated by an electric motor, said pump head having an inletand an outlet, and said pump inlet in fluid communication with saidreservoir outlet said electric motor is controlled by an amplifiercontroller, said amplifier controller supplying a constant current tosaid pump head thereby causing said pump head to supply a relativelyconstant pressure to said fluid in said second fluid supply line; asecond fluid supply line, said second fluid supply line in fluidcommunication with said pump outlet for receiving fluid pumped out ofsaid pump outlet; an external fluid source, said external fluid sourcein fluid communication with said reservoir, and a pressure damper, saidpressure damper in fluid communication with said pump outlet.